Psychiatric Effects of Cannabis 8p

7/29/2019 Psychiatric Effects of Cannabis 8p

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BackgroundBackground Cannabis is commonlyCannabis is commonly

regarded as aninnocuous drugand theregarded as an innocuous drugand the

prevalence of lifetime and regular usehasprevalence of lifetime and regular usehas

increased in mostdeveloped countries.increased in mostdeveloped countries.

However, accumulative evidenceHowever, accumulative evidence

highlights the risks of dependence andhighlights the risks of dependence and

other adverse effects, particularly amongother adverse effects, particularly among

people with pre-existingpsychiatricpeople with pre-existingpsychiatric

disorders.disorders.

AimsAims To re-evaluate the adverse effectsTo re-evaluate theadverse effects

of cannabis inthe general population andof cannabis inthe general population and

among vulnerable individuals, includingamong vulnerable individuals, including

those with serious psychiatric disorders.those with serious psychiatric disorders.

MethodMethod Awide-ranging reviewoftheAwide-ranging reviewofthe

topics related tothese issues.topics relatedtotheseissues.

Results and conclusionsResults and conclusions AnAn

appreciable proportion of cannabisusersappreciable proportion of cannabisusers

report short-lived adverse effects,report short-lived adverse effects,

includingpsychotic states followingheavyincludingpsychotic states followingheavy

consumption, and regular users are at riskconsumption, and regular users are at risk

of dependence.People with major mentalof dependence.People with major mental

illnesses such as schizophrenia areillnesses such as schizophrenia are

especially vulnerableinthatcannabisespecially vulnerableinthatcannabis

generallyprovokes relapse and aggravatesgenerallyprovokes relapse and aggravates

existing symptoms.Health workers needexisting symptoms.Healthworkers need

to recognise, and respond to, the adverseto recognise, and respondto, the adverse

effects ofcannabis on mentalhealth.effects ofcannabis on mentalhealth.

Declaration of interestDeclaration of interest ThisreviewThis review

was commissioned and funded by thewas commissioned and funded by the

Department of Health, butthe findingsDepartment of Health, butthe findings

are those ofthe author alone.are those ofthe author alone.

UNTOWARD MENTALUNTOWARD MENTAL

EFFECTS OF CANNABISEFFECTS OF CANNABIS

The untoward mental effects of cannabisThe untoward mental effects of cannabis

may be classified:may be classified:

(a)(a) Psychological responses such as panic,Psychological responses such as panic,

anxiety, depression or psychosis.anxiety, depression or psychosis.

These effects may be described asThese effects may be described as

`toxic' in that they generally relate to`toxic' in that they generally relate to

excess consumption of the drug.excess consumption of the drug.

(b)(b) Effects of cannabis on pre-existingEffects of cannabis on pre-existing

mental illness and cannabis as a risk-mental illness and cannabis as a risk-

factor for mental illness.factor for mental illness.

(c)(c) Dependency or withdrawal effects.Dependency or withdrawal effects.

The effects of cannabis on cognition areThe effects of cannabis on cognition are

separately reviewed by Ashton (2001, thisseparately reviewed by Ashton (2001, this

issue).issue).

PSYCHOLOGICALPSYCHOLOGICALRESPONSES TO CANNABISRESPONSES TO CANNABIS

There is good evidence that taking cannabisThere is good evidence that taking cannabis

leads to acute adverse mental effects in aleads to acute adverse mental effects in a

high proportion of regular users. Many ofhigh proportion of regular users. Many of

these effects are dose-related, but adversethese effects are dose-related, but adverse

symptoms may be aggravated by con-symptoms may be aggravated by con-

stitutional factors including youthfulness,stitutional factors including youthfulness,

personality attributes and vulnerability topersonality attributes and vulnerability to

serious mental illness.serious mental illness.

Cannabis and mood changeCannabis and mood change

The acute response to cannabis generallyThe acute response to cannabis generallyincludes euphoria and feelings of detach-includes euphoria and feelings of detach-

ment and relaxation. Adverse effects arement and relaxation. Adverse effects are

not uncommon: these are generally short-not uncommon: these are generally short-

lived, but may persist or recur withlived, but may persist or recur with

continued use of the drug.continued use of the drug.

From New Zealand, a sample of 1000From New Zealand, a sample of 1000

people aged 1825 were asked to completepeople aged 1825 were asked to complete

a self-administered questionnaire ona self-administered questionnaire on

cannabis use and related problemscannabis use and related problems

(Thomas, 1996). Those respondents who(Thomas, 1996). Those respondents who

admitted using cannabis (38%) were askedadmitted using cannabis (38%) were asked

about mental health consequences; of these,about mental health consequences; of these,

22% reported panic attacks or anxiety.22% reported panic attacks or anxiety.Women were twice as likely as men toWomen were twice as likely as men to

report these symptoms. Troisireport these symptoms. Troisi et alet al (1998)(1998)

used urine tests on Italian draftees toused urine tests on Italian draftees to

identify 133 men who used only cannabis.identify 133 men who used only cannabis.

All individuals with a pre-existing psychosisAll individuals with a pre-existing psychosis

or severe personality disorder had beenor severe personality disorder had been

excluded. An adjustment disorder withexcluded. An adjustment disorder with

depressed mood was found in 16%, majordepressed mood was found in 16%, majordepression in 14%, and dysthymia indepression in 14%, and dysthymia in

10.5%. The severity of these symptoms10.5%. The severity of these symptoms

was dose-related. No acute psychoticwas dose-related. No acute psychotic

symptoms were reported. Reillysymptoms were reported. Reilly et al et al

(1998) describe the adverse effects found(1998) describe the adverse effects found

among 268 cannabis users who had takenamong 268 cannabis users who had taken

the drug for at least 10 years, and who con-the drug for at least 10 years, and who con-

tinued to smoke about two refers a day.tinued to smoke about two refers a day.

The most common adverse effects wereThe most common adverse effects were

feelings of anxiety, paranoia or depressionfeelings of anxiety, paranoia or depression

(21%), tiredness and low motivation(21%), tiredness and low motivation

(21%).(21%).

Among individuals making seriousAmong individuals making seriousattempts at suicide, 16.2% met criteria forattempts at suicide, 16.2% met criteria for

cannabis misuse/dependence comparedcannabis misuse/dependence compared

with 1.9% of controls much of the highlywith 1.9% of controls much of the highly

significant association was thought to besignificant association was thought to be

due to independent variables including co-due to independent variables including co-

morbidity, but it is suggested that cannabismorbidity, but it is suggested that cannabis

misuse makes a direct contribution to themisuse makes a direct contribution to the

risk of serious self-harm, either directly orrisk of serious self-harm, either directly or

by aggravation of other mental disordersby aggravation of other mental disorders

(Beautrais(Beautrais et alet al, 1999)., 1999).

Cannabis and psychosisCannabis and psychosisCannabis use can lead to a range of short-Cannabis use can lead to a range of short-

lived symptoms such as depersonalisation,lived symptoms such as depersonalisation,

derealisation, a feeling of loss of control,derealisation, a feeling of loss of control,

fear of dying, irrational panic and para-fear of dying, irrational panic and para-

noid ideas (Thomas, 1993). For example,noid ideas (Thomas, 1993). For example,

Thomas (1996) reported that, amongThomas (1996) reported that, among

cannabis users who responded to his sur-cannabis users who responded to his sur-

vey, 15% identified psychotic symptomsvey, 15% identified psychotic symptoms

such as hearing voices or having un-such as hearing voices or having un-

warranted feelings of persecution or riskwarranted feelings of persecution or risk

of harmof harm from others. Two small case stu-from others. Two small case stu-

dies have reported prolonged depersonal-dies have reported prolonged depersonal-

isation after cessation of cannabis useisation after cessation of cannabis use(Szymanski, 1981; Keshaven & Lishman,(Szymanski, 1981; Keshaven & Lishman,

1986). `Flashbacks' or the subsequent1986). `Flashbacks' or the subsequent

partial re-experience when drug-free ofpartial re-experience when drug-free of

symptoms experienced during intoxicationsymptoms experienced during intoxication

are rarely reported after cannabis useare rarely reported after cannabis use

(Thomas, 1993).(Thomas, 1993).

The casual use of the term `cannabisThe casual use of the term `cannabis

psychosis' in clinical psychiatric practicepsychosis' in clinical psychiatric practice

and in the scientific literature results inand in the scientific literature results in

diagnostic imprecision and research ofdiagnostic imprecision and research of

uncertain validity. Thornicroft (1990) re-uncertain validity. Thornicroft (1990) re-

views the possible associations betweenviews the possible associations between

cannabis use and psychosis and suggestscannabis use and psychosis and suggeststhat common methodological failings are:that common methodological failings are:

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B R I T I S H J O U R N A L O F P S Y C H I A T RYB R I T I S H J O U R N A L O F P S Y C H I A T RY ( 2 0 0 1 ) , 1 7 8 , 1 1 6 ^ 1 2 2( 2 0 0 1 ) , 1 7 8 , 1 1 6 ^ 1 2 2

Psychiatric effects of cannabisPsychiatric effects of cannabis{{

ANDREW JOHNSANDREW JOHNS

{{See editorial, p.9 8, thisissue.See editorial, p.9 8, thisissue.


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P S Y C HI A T R I C E F F E C T S O F C A N N A B I SP S Y C H IA T R I C E F F E C T S O F C A N N A B I S

(a) studies fail to adequately separate or-(a) studies fail to adequately separate or-

ganic from functional psychotic reactionsganic from functional psychotic reactions

to cannabis; (b) they have insufficiently dis-to cannabis; (b) they have insufficiently dis-

criminated between psychotic symptomscriminated between psychotic symptoms

and syndromes of a psychosis; and (c) theyand syndromes of a psychosis; and (c) they

have not balanced the weight of evidencehave not balanced the weight of evidence

for and against the category of cannabisfor and against the category of cannabispsychosis. Although there is good evidencepsychosis. Although there is good evidence

for believing that cannabis use may infor believing that cannabis use may in

certaincertain circumstances contribute tocircumstances contribute to

psychotic disorders, the connections arepsychotic disorders, the connections are

complex.complex.

HallHall et alet al(1994) suggest that the funda-(1994) suggest that the funda-

mental questions are: is there a cannabismental questions are: is there a cannabis

psychosis, and does cannabis precipitatepsychosis, and does cannabis precipitate

an underlying psychosis? In theory, canna-an underlying psychosis? In theory, canna-

bis use may precipitate a psychosis in thebis use may precipitate a psychosis in the

following ways.following ways.

(a)(a) Acute use of large doses of the drugAcute use of large doses of the drug

may induce a toxic or organic psychosismay induce a toxic or organic psychosis

with symptoms of confusion and hallu-with symptoms of confusion and hallu-

cination, which remit on abstinence.cination, which remit on abstinence.

(b)(b) Cannabis use may lead to an acuteCannabis use may lead to an acute

functional psychosis, similar to anfunctional psychosis, similar to an

acute schizophreniform state andacute schizophreniform state and

lacking the organic features of a toxiclacking the organic features of a toxic

psychosis.psychosis.

(c)(c) Cannabis use may lead to a chronicCannabis use may lead to a chronic

psychosis, which persists after absti-psychosis, which persists after absti-

nence.nence.

(d)(d) Long-term cannabis use may lead to anLong-term cannabis use may lead to an

organic psychosis which only partiallyorganic psychosis which only partiallyremits after abstinence, leaving aremits after abstinence, leaving a

residual deficit state, sometimes calledresidual deficit state, sometimes called

an amotivational syndrome, which isan amotivational syndrome, which is

thought to be analogous to the chronicthought to be analogous to the chronic

organic brain syndrome seen afterorganic brain syndrome seen after

prolonged misuse of alcohol.prolonged misuse of alcohol.

(e)(e) Cannabis use may be a risk-factorCannabis use may be a risk-factor

for serious mental illness such asfor serious mental illness such as

schizophrenia.schizophrenia.

Cannabis and toxic psychosisCannabis and toxic psychosis

Apart from single-case reports, the natureApart from single-case reports, the nature

of cannabis-induced toxic psychosis isof cannabis-induced toxic psychosis isconsidered in the following studies, all ofconsidered in the following studies, all of

which are weakened by the lack of urine-which are weakened by the lack of urine-

testing to confirm the presence of cannabistesting to confirm the presence of cannabis

and the absence of other drugs of misuse.and the absence of other drugs of misuse.

Talbott & Teague (1969) described 12Talbott & Teague (1969) described 12

soldiers in Vietnam who, after their firstsoldiers in Vietnam who, after their first

admitted use of cannabis, showed dis-admitted use of cannabis, showed dis-

orientation, impaired memory, confusion,orientation, impaired memory, confusion,

reduced attention span and disorderedreduced attention span and disordered

thinking with labile effect and hallu-thinking with labile effect and hallu-

cinations. These symptoms resolved withincinations. These symptoms resolved within

a week. Tennant & Groesbeck (1972)a week. Tennant & Groesbeck (1972)

describe psychoses among 36000 USdescribe psychoses among 36000 USservicemen stationed in Germany. Of theservicemen stationed in Germany. Of the

5120 soldiers using cannabis at least three5120 soldiers using cannabis at least three

timestimes a week, 720 presented witha week, 720 presented with

cannabis-cannabis-related problems. The hashishrelated problems. The hashish

available was potent, containing 510%available was potent, containing 510%

tetrahydrocannabinol (THC). The authorstetrahydrocannabinol (THC). The authors

identified 19 cases of a panic attack oridentified 19 cases of a panic attack or

short-lived toxic psychosis, which appearedshort-lived toxic psychosis, which appearedafter a single high dose of hashish, and aafter a single high dose of hashish, and a

further 85 cases of toxic psychosis whichfurther 85 cases of toxic psychosis which

appeared after the consumption of cannabisappeared after the consumption of cannabis

with other drugs. These acute states tendedwith other drugs. These acute states tended

to resolve within 3 days.to resolve within 3 days.

From Calcutta, Chopra & Smith (1974)From Calcutta, Chopra & Smith (1974)

retrospectively identified 200 in-patientsretrospectively identified 200 in-patients

who showed serious psychiatric symptomswho showed serious psychiatric symptoms

after taking cannabis. The most commonafter taking cannabis. The most common

symptoms in all patients were suddensymptoms in all patients were sudden

onset of confusion, often associated withonset of confusion, often associated with

hallucinations and emotional lability.hallucinations and emotional lability.

Disorientation, depersonalisation andDisorientation, depersonalisation andparanoid symptoms were common. Manyparanoid symptoms were common. Many

patients had taken a large dose of cannabis,patients had taken a large dose of cannabis,

which was followed by an intoxicated statewhich was followed by an intoxicated state

for which they were subsequently amnesic.for which they were subsequently amnesic.

Among the 34% of patients without aAmong the 34% of patients without a

previous history of psychiatric disorder,previous history of psychiatric disorder,

adverse symptoms lasted no more than aadverse symptoms lasted no more than a

few days, followed by full recovery. A pre-few days, followed by full recovery. A pre-

vious history of schizophrenia or person-vious history of schizophrenia or person-

ality disorder was associated with longerality disorder was associated with longer

duration of adverse symptoms.duration of adverse symptoms.

From Pakistan, ChaudryFrom Pakistan, Chaudry et alet al (1991)(1991)

report on effects ofreport on effects of bhangbhang, a potent, a potentbeverage made from an infusion of canna-beverage made from an infusion of canna-

bis leaves and flowering tops. They identi-bis leaves and flowering tops. They identi-

fied 15 patients who having takenfied 15 patients who having taken bhangbhang,,

presented with a psychosis with symptomspresented with a psychosis with symptoms

of grandiosity, excitement, hostility, dis-of grandiosity, excitement, hostility, dis-

orientation, hallucinations and thoughtorientation, hallucinations and thought

disorder. Mental state was assessed system-disorder. Mental state was assessed system-

atically, using the Brief Psychiatric Ratingatically, using the Brief Psychiatric Rating

Scale (BPRS) (LukoffScale (BPRS) (Lukoff et alet al, 1986). The, 1986). The

control group of 10 patients all usedcontrol group of 10 patients all used bhangbhang,,

but less frequently than the study group.but less frequently than the study group.

This work suggests that cannabis,This work suggests that cannabis,

especially in high doses, can produce aespecially in high doses, can produce atoxic psychosis in individuals who havetoxic psychosis in individuals who have

no history of severe mental illness. Theno history of severe mental illness. The

main features are mild impairment of con-main features are mild impairment of con-

sciousness, distorted sense of passage ofsciousness, distorted sense of passage of

time, dream-like euphoria, progressing totime, dream-like euphoria, progressing to

fragmented thought processes and halluci-fragmented thought processes and halluci-

nations, generally resolving within a weeknations, generally resolving within a week

of abstinence (Lishman, 1998).of abstinence (Lishman, 1998).

Cannabis and acute functionalCannabis and acute functional

psychosispsychosis

A number of studies suggest that heavyA number of studies suggest that heavycannabis use can lead to an acute functionalcannabis use can lead to an acute functional

illness, that is a state resembling the psy-illness, that is a state resembling the psy-

chosis of acute schizophrenia without thechosis of acute schizophrenia without the

amnesia and confusion of a toxic psychosis.amnesia and confusion of a toxic psychosis.

Tennant & Groesbeck (1972) identifiedTennant & Groesbeck (1972) identified

115 cases of schizophrenic reaction among115 cases of schizophrenic reaction among

the 720 regular users of cannabis; however,the 720 regular users of cannabis; however,

all but three had used cannabis with otherall but three had used cannabis with otherdrugs or alcohol. Thacore & Shukladrugs or alcohol. Thacore & Shukla

(1976) compared 25 individuals with a(1976) compared 25 individuals with a

putative diagnosis of `cannabis psychosisputative diagnosis of `cannabis psychosis

of the paranoid type' with controls diag-of the paranoid type' with controls diag-

nosed with paranoid schizophrenia.nosed with paranoid schizophrenia.

Patients with cannabis psychosis showedPatients with cannabis psychosis showed

more bizarre behaviour, violence, panickymore bizarre behaviour, violence, panicky

affect, more insight and less evidence ofaffect, more insight and less evidence of

thought disorder. They also showed a rapidthought disorder. They also showed a rapid

response to neuroleptics with completeresponse to neuroleptics with complete

recovery. More robust in methodology isrecovery. More robust in methodology is

the work of Rottanburgthe work of Rottanburg et alet al (1982) in(1982) in

which 20 patients with psychosis and withwhich 20 patients with psychosis and withhigh urinary cannabinoids were comparedhigh urinary cannabinoids were compared

with 20 matched cannabis-free controls.with 20 matched cannabis-free controls.

Mental state was assessed using the PresentMental state was assessed using the Present

State Examination (PSE) (WingState Examination (PSE) (Wing et al et al ,,

1974). The cannabis-positive patients had1974). The cannabis-positive patients had

more symptoms of hypomania andmore symptoms of hypomania and

agitation, less auditory hallucinations,agitation, less auditory hallucinations,

flattening of affect, incoherent speech andflattening of affect, incoherent speech and

hysteria than controls. Clouding of con-hysteria than controls. Clouding of con-

sciousness was absent in most cannabissciousness was absent in most cannabis

patients. They also showed markedpatients. They also showed marked

improvements in symptoms within a week,improvements in symptoms within a week,

while the controls remained unwell despitewhile the controls remained unwell despitereceiving comparable antipsychotic drugs.receiving comparable antipsychotic drugs.

The authors conclude that a high intakeThe authors conclude that a high intake

of cannabis may be related to a rapidly re-of cannabis may be related to a rapidly re-

solving psychosis with marked hypomanicsolving psychosis with marked hypomanic

features. However, 16 cannabis-positivefeatures. However, 16 cannabis-positive

psychotic patients left the study pre-psychotic patients left the study pre-

maturely, which may bias the findings onmaturely, which may bias the findings on

the 20 who remained. Rapid resolution ofthe 20 who remained. Rapid resolution of

symptoms is also reported by Carneysymptoms is also reported by Carney et alet al

(1984), who identified nine patients with(1984), who identified nine patients with

cannabis-related psychotic episodes. Theircannabis-related psychotic episodes. Their

differing symptomatology was describeddiffering symptomatology was described

as `schizophreniform, manic, delusionalas `schizophreniform, manic, delusionalpsychosis and confusion'.psychosis and confusion'.

More recently, Mathers & GhodseMore recently, Mathers & Ghodse

(1992) carried out a prospective study of(1992) carried out a prospective study of

in-patients with psychotic symptoms andin-patients with psychotic symptoms and

cannabis-positive urine. Blind to the urinecannabis-positive urine. Blind to the urine

test result, researchers applied the PSE ontest result, researchers applied the PSE on

admission and again at 1 and 6 months.admission and again at 1 and 6 months.

Concurrently admitted patients with psy-Concurrently admitted patients with psy-

chosis but with drug-free urine analysischosis but with drug-free urine analysis

were controls. At 1 week the two groupswere controls. At 1 week the two groups

differed significantly on only five PSEdiffered significantly on only five PSE

items: changed perception, thought inser-items: changed perception, thought inser-

tion, non-verbal auditory hallucinations,tion, non-verbal auditory hallucinations,delusions of control, and delusions ofdelusions of control, and delusions of

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grandiose ability; this symptom cluster at 1grandiose ability; this symptom cluster at 1

week was thought to be consistent withweek was thought to be consistent with

acute cannabis intoxication. These differ-acute cannabis intoxication. These differ-

ences were minor at 1 month and absentences were minor at 1 month and absent

at 6 months. Chronic cannabis-inducedat 6 months. Chronic cannabis-induced

psychosis was not found. Caucasianpsychosis was not found. Caucasian

patients were more likely to be depressedpatients were more likely to be depressedwith depersonalisation and derealisation,with depersonalisation and derealisation,

while Africanwhile AfricanCaribbeans showed moreCaribbeans showed more

culturally influenced delusions. However,culturally influenced delusions. However,

these findings could not be replicated bythese findings could not be replicated by

McGuireMcGuire et alet al (1994) who also used the(1994) who also used the

PSE to assess the psychopathology of 23PSE to assess the psychopathology of 23

patients with psychosis who were cannabis-patients with psychosis who were cannabis-

positive on urinary screening, and 46positive on urinary screening, and 46

matched drug-free controls. Cases andmatched drug-free controls. Cases and

controls were indistinguishable in terms ofcontrols were indistinguishable in terms of

psychopathology, DSMIII diagnosespsychopathology, DSMIII diagnoses

(American Psychiatric Association, 1980),(American Psychiatric Association, 1980),

onset of recent illness, the proportion ofonset of recent illness, the proportion offfirst admissions, ethnicity and socio-irst admissions, ethnicity and socio-

economic class, differing only in theireconomic class, differing only in their

histories of substance use.histories of substance use.

Having compared groups of drug-Having compared groups of drug-

misusing patients with psychosis of varyingmisusing patients with psychosis of varying

duration, Tsuangduration, Tsuang et alet al (1982) concluded(1982) concluded

that the shorter-duration disorders werethat the shorter-duration disorders were

drug-induced toxic psychoses, and thedrug-induced toxic psychoses, and the

longer-lasting disorders represented thelonger-lasting disorders represented the

expression of functional psychiatric illnessexpression of functional psychiatric illness

in vulnerable individuals. If corroborated,in vulnerable individuals. If corroborated,

this suggests that the `functional psychosis'this suggests that the `functional psychosis'

related to cannabis use is best explained asrelated to cannabis use is best explained asa precipitated episode of an underlyinga precipitated episode of an underlying

functional illness.functional illness.

Cannabis and chronic psychosisCannabis and chronic psychosis

Ghodse (1986) has suggested that regularGhodse (1986) has suggested that regular

heavy users of cannabis may suffer repeatedheavy users of cannabis may suffer repeated

short episodes of psychosis and effectivelyshort episodes of psychosis and effectively

`maintain' themselves in a chronic psy-`maintain' themselves in a chronic psy-

chotic state. This is a possibility, but Hallchotic state. This is a possibility, but Hall

et alet al(1994) note that it is difficult to distin-(1994) note that it is difficult to distin-

guish between a chronic cannabis psychosisguish between a chronic cannabis psychosis

and the co-occurrence of an illness such asand the co-occurrence of an illness such asschizophrenia with continued cannabisschizophrenia with continued cannabis

use. There is however, no robust evidenceuse. There is however, no robust evidence

that heavy cannabis use may lead to a psy-that heavy cannabis use may lead to a psy-

chotic illness which persists after abstinencechotic illness which persists after abstinence

(Thomas, 1993).(Thomas, 1993).

Cannabis and amotivationalCannabis and amotivational

syndromesyndrome

It has been suggested that heavy cannabisIt has been suggested that heavy cannabis

use could lead to an `amotivational syn-use could lead to an `amotivational syn-

drome' described as personality deterio-drome' described as personality deterio-

rationration with loss of energy and drive towith loss of energy and drive towork (Tennant & Groesbeck, 1972). Thework (Tennant & Groesbeck, 1972). The

supporting evidence largely comprises un-supporting evidence largely comprises un-

controlled studies of long-term cannabiscontrolled studies of long-term cannabis

users in various cultures (Hallusers in various cultures (Hall et al et al ,,

1994). It is probable that amotivational1994). It is probable that amotivational

syndrome represents nothing more thansyndrome represents nothing more than

ongoing intoxication in frequent users ofongoing intoxication in frequent users of

the drug (Negretethe drug (Negrete et alet al, 1986) and the valid-, 1986) and the valid-ity of this diagnosis remains uncertain (Hallity of this diagnosis remains uncertain (Hall

et alet al, 1994)., 1994).

Cannabis as risk-factor for seriousCannabis as risk-factor for serious

mentall illnessmentall illness

Comorbidity ratesComorbidity rates

Cannabis use is associated with high ratesCannabis use is associated with high rates

of comorbidity for other psychiatric diag-of comorbidity for other psychiatric diag-

noses. The Epidemiologic Catchment Areanoses. The Epidemiologic Catchment Area

(ECA) survey (Regier(ECA) survey (Regier et al et al , 1990) of, 1990) of

20000 subjects in community and in-20000 subjects in community and in-

stitutional settings showed that 50.1% ofstitutional settings showed that 50.1% ofindividualsindividuals with cannabis dependence/with cannabis dependence/

misusemisuse also met DSMIII criteria for onealso met DSMIII criteria for one

other non-drug or alcohol mental disorder.other non-drug or alcohol mental disorder.

Among 133 Italian draftees, TroisiAmong 133 Italian draftees, Troisi et alet al

(1998) found that the prevalence of co-(1998) found that the prevalence of co-

morbidity was significantly related to themorbidity was significantly related to the

pattern of cannabis use: 69% of subjectspattern of cannabis use: 69% of subjects

with DSMIIIR cannabis dependence,with DSMIIIR cannabis dependence,

41% of those with cannabis abuse and41% of those with cannabis abuse and

24% of occasional users reported at least24% of occasional users reported at least

one DSMIIIR Axis 1 psychiatric diag-one DSMIIIR Axis 1 psychiatric diag-

nosis. Most common were adjustment dis-nosis. Most common were adjustment dis-

order with depressed mood (order with depressed mood (nn21), major21), majordepression (depression (nn19) and dysthymia (19) and dysthymia (nn14).14).

The severity of symptoms also increasedThe severity of symptoms also increased

with degree of cannabis use. Psychoticwith degree of cannabis use. Psychotic

symptoms were not found, but it shouldsymptoms were not found, but it should

be noted all individuals with psychotic ill-be noted all individuals with psychotic ill-

ness or severe personality disorder wereness or severe personality disorder were

not drafted.not drafted.

There are high rates of drug misuseThere are high rates of drug misuse

among people with mental illness. Theamong people with mental illness. The

ECA study (RegierECA study (Regier et alet al, 1990) showed that, 1990) showed that

the risk of meeting criteria for a substancethe risk of meeting criteria for a substance

misuse disorder was 4.6 times higher inmisuse disorder was 4.6 times higher in

those suffering from schizophrenia than inthose suffering from schizophrenia than inthe general population. Schizophrenia wasthe general population. Schizophrenia was

associated with a six-fold increase in riskassociated with a six-fold increase in risk

of developing a drug use disorder, and can-of developing a drug use disorder, and can-

nabisnabis was the most commonly misusedwas the most commonly misused

drug.drug. MenezesMenezes et alet al (1996) examined the(1996) examined the

prevalence of substance misuse problemsprevalence of substance misuse problems

among 171 patients with psychotic illnessamong 171 patients with psychotic illness

who had any contact with mental healthwho had any contact with mental health

treatment services in a south London area.treatment services in a south London area.

Alcohol problems were more prevalent,Alcohol problems were more prevalent,

but current use of one or more drugs wasbut current use of one or more drugs was

found in 35 subjects (20%); all but two saidfound in 35 subjects (20%); all but two said

they used cannabis. Cantwellthey used cannabis. Cantwell et alet al (1999)(1999)studied 168 subjects presenting with a firststudied 168 subjects presenting with a first

episode of psychosis and found 1-year pre-episode of psychosis and found 1-year pre-

valence rates of 19.5% for drug misuse,valence rates of 19.5% for drug misuse,

11.7% for alcohol misuse, and cannabis11.7% for alcohol misuse, and cannabis

was the most commonly misused substance.was the most commonly misused substance.

Given these findings, it is necessary toGiven these findings, it is necessary to

review the possible role of cannabis as areview the possible role of cannabis as a

risk factor for functional illness and forrisk factor for functional illness and forthe aggravation of symptoms.the aggravation of symptoms.

Effects of cannabis on severe mental illnessEffects of cannabis on severe mental illness

Given that high doses of cannabis can causeGiven that high doses of cannabis can cause

a toxic psychosis, then it may be supposeda toxic psychosis, then it may be supposed

it will aggravate the symptoms of schizo-it will aggravate the symptoms of schizo-

phrenia. However, clinical experience sug-phrenia. However, clinical experience sug-

gests that some patients say that they takegests that some patients say that they take

cannabis as a form of `self-medication'.cannabis as a form of `self-medication'.

For example, DixonFor example, Dixon et alet al (1990) inter-(1990) inter-

viewed 83 patients with schizophrenia orviewed 83 patients with schizophrenia or

schizophreniform psychoses who reportedschizophreniform psychoses who reportedthat cannabis reduced anxiety and depres-that cannabis reduced anxiety and depres-

sion, led to increased suspiciousness andsion, led to increased suspiciousness and

had varied effects on drive and hallucina-had varied effects on drive and hallucina-

tions. Arndttions. Arndt et alet al (1992) investigated a(1992) investigated a

cohort of 131 patients with schizophreniacohort of 131 patients with schizophrenia

and found that previous use of cannabisand found that previous use of cannabis

had no impact on current symptoms.had no impact on current symptoms.

Peralta & Cuesta (1992) reported thatPeralta & Cuesta (1992) reported that

cannabis had no significant effect oncannabis had no significant effect on

positive symptoms of schizophrenia, but itpositive symptoms of schizophrenia, but it

did attenuate negative symptoms.did attenuate negative symptoms.

On the other hand, there are a few con-On the other hand, there are a few con-

trolled studies that have tended to demon-trolled studies that have tended to demon-strate that cannabis aggravates the severitystrate that cannabis aggravates the severity

of positive symptoms. Negreteof positive symptoms. Negrete et alet al (1986)(1986)

described the history of confirmed cannabisdescribed the history of confirmed cannabis

use in 137 patients with schizophrenia inuse in 137 patients with schizophrenia in

treatment. Subjects who were using canna-treatment. Subjects who were using canna-

bis over the 6-month observation periodbis over the 6-month observation period

presented with significantly greaterpresented with significantly greater

delusions and hallucinations, and madedelusions and hallucinations, and made

more use of psychiatric services. Similarly,more use of psychiatric services. Similarly,

CleghornCleghorn et alet al(1991) found that drug-users(1991) found that drug-users

with schizophrenia, among whom cannabiswith schizophrenia, among whom cannabis

was the most heavily used drug, had a high-was the most heavily used drug, had a high-

er prevalence of hallucinations, delusionser prevalence of hallucinations, delusionsand other positive symptoms. This findingand other positive symptoms. This finding

was replicated by Baigentwas replicated by Baigent et alet al (1995),(1995),

who reported that among 53 in-patientswho reported that among 53 in-patients

with a dual diagnosis of substance misusewith a dual diagnosis of substance misuse

and schizophrenia, cannabis was the onlyand schizophrenia, cannabis was the only

drug that worsened positive symptoms.drug that worsened positive symptoms.

Data from the ECA survey (SwansonData from the ECA survey (Swanson

et alet al, 1990) also casts some light on the, 1990) also casts some light on the

possible effects of cannabis use disorderpossible effects of cannabis use disorder

and violence. Subjects were asked aboutand violence. Subjects were asked about

episodes of violence in the previous yearepisodes of violence in the previous year

(i.e. hitting a partner, bruising a child,(i.e. hitting a partner, bruising a child,

fighting, using a weapon in a fight whilefighting, using a weapon in a fight whiledrinking). Of the 191 respondents withdrinking). Of the 191 respondents with

11 811 8


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cannabis abuse or dependence, 19.25%cannabis abuse or dependence, 19.25%

(risk ratio 9.4) had been violent compared(risk ratio 9.4) had been violent compared

with 12.69% (risk ratio 6.2) of those withwith 12.69% (risk ratio 6.2) of those with

schizophrenia or schizophreniform dis-schizophrenia or schizophreniform dis-

order and 24.57% (risk ratio 11.9) oforder and 24.57% (risk ratio 11.9) of

those with alcohol abuse or dependence.those with alcohol abuse or dependence.

Here, the risk is expressed relative to theHere, the risk is expressed relative to the2.05% who were violent among those of2.05% who were violent among those of

the sample population who showed nothe sample population who showed no

psychiatric disorder. However, this doespsychiatric disorder. However, this does

not amount to a causal correlation betweennot amount to a causal correlation between

cannabis co-morbidity and violence, givencannabis co-morbidity and violence, given

the possible role of intervening variablesthe possible role of intervening variables

such as individual and social factors.such as individual and social factors.

That cannabis consumption also has anThat cannabis consumption also has an

adverse effect on the course of schizo-adverse effect on the course of schizo-

phrenia was noted by Negretephrenia was noted by Negrete et alet al (1986)(1986)

and confirmed in a prospective study byand confirmed in a prospective study by

LinszmanLinszman et alet al (1994). A cohort of newly(1994). A cohort of newly

admitted patients with schizophrenia wereadmitted patients with schizophrenia wereassessed monthly for a year, using theassessed monthly for a year, using the

BPRS and self-reports of cannabis use. TheBPRS and self-reports of cannabis use. The

cannabis-using group (cannabis-using group (nn24) experienced24) experienced

significantly more and earlier psychoticsignificantly more and earlier psychotic

relapses and this effect was dose-related.relapses and this effect was dose-related.

As HallAs Hall et alet al(1994) remark, these find-(1994) remark, these find-

ings are a slender basis on which to drawings are a slender basis on which to draw

conclusions about the effect of cannabisconclusions about the effect of cannabis

on schizophrenic symptoms. Until furtheron schizophrenic symptoms. Until further

prospective studies have been carried out,prospective studies have been carried out,

it would be prudent to regard cannabis asit would be prudent to regard cannabis as

a vulnerability factor in relation to majora vulnerability factor in relation to major

mental illness and to caution at-riskmental illness and to caution at-riskindividuals against using the drug.individuals against using the drug.

Cannabis as risk factor for mental illnessCannabis as risk factor for mental illness

There is no evidence that cannabis is a cau-There is no evidence that cannabis is a cau-

sal factor in schizophrenia and it is moresal factor in schizophrenia and it is more

relevant to consider whether the misuse ofrelevant to consider whether the misuse of

the drug constitutes a risk factor for thisthe drug constitutes a risk factor for this

illness. Supporting evidence is found in aillness. Supporting evidence is found in a

prospective study by Andreassonprospective study by Andreasson et al et al

(1987) of 45 570 Swedish conscripts, of(1987) of 45 570 Swedish conscripts, of

whom 9.4% had used cannabis and 1.7%whom 9.4% had used cannabis and 1.7%

were `high consumers' having used morewere `high consumers' having used morethan 50 times. Fifteen-year follow-up datathan 50 times. Fifteen-year follow-up data

were drawn from national registers ofwere drawn from national registers of

deaths and psychiatric cases. Compareddeaths and psychiatric cases. Compared

with non-users, the relative risk of schizo-with non-users, the relative risk of schizo-

phrenia was 2.4 in the group that reportedphrenia was 2.4 in the group that reported

use of cannabis at least once, rising to 6.0use of cannabis at least once, rising to 6.0

among heavy users. Nearly half (430/730)among heavy users. Nearly half (430/730)

of these high consumers had a psychiatricof these high consumers had a psychiatric

diagnosis other than psychosis on conscrip-diagnosis other than psychosis on conscrip-

tion; controlling for this reduced the rela-tion; controlling for this reduced the rela-

tive risk to 2.9. The authors suggest thattive risk to 2.9. The authors suggest that

cannabis consumption is a `life-event stres-cannabis consumption is a `life-event stres-

sor' for individuals vulnerable to schizo-sor' for individuals vulnerable to schizo-phrenia. Hallphrenia. Hall et alet al (1994) offer a number(1994) offer a number

of alternative explanations. There is a largeof alternative explanations. There is a large

temporal gap between self-reported canna-temporal gap between self-reported canna-

bis use on conscription and the develop-bis use on conscription and the develop-

ment of schizophrenia over 15 years, andment of schizophrenia over 15 years, and

no data as to whether the cannabis use con-no data as to whether the cannabis use con-

tinued during this time. Drugs other thantinued during this time. Drugs other than

cannabis could have been taken at any timecannabis could have been taken at any timeafter conscription.after conscription.

It should also be noted that as only 49 ofIt should also be noted that as only 49 of

the 274 conscripts with schizophrenia hadthe 274 conscripts with schizophrenia had

ever tried cannabis, then this drug may onlyever tried cannabis, then this drug may only

be relevant to a minority of cases. Further-be relevant to a minority of cases. Further-

more, Jablenskymore, Jablensky et alet al (1992) demonstrate a(1992) demonstrate a

striking uniformity in the incidence ofstriking uniformity in the incidence of

schizophrenia in cultures with very differentschizophrenia in cultures with very different

rates of cannabis consumption.rates of cannabis consumption.

The possibility of a genetic explanationThe possibility of a genetic explanation

for the association between cannabis usefor the association between cannabis use

and schizophrenia was raised by McGuireand schizophrenia was raised by McGuire

et alet al (1994). In this study, 23 patients with(1994). In this study, 23 patients withpsychosis and with cannabis in their urinepsychosis and with cannabis in their urine

were gender-matched with 46 drug-freewere gender-matched with 46 drug-free

controls with psychosis, and the lifetimecontrols with psychosis, and the lifetime

risk of psychiatric disorder among all therisk of psychiatric disorder among all the

first-degree relatives was ascertained. Thefirst-degree relatives was ascertained. The

cannabis-positive subjects had a signifi-cannabis-positive subjects had a signifi-

cantly greater (7.1%) familial risk ofcantly greater (7.1%) familial risk of

schizophrenia than controls (0.7%),schizophrenia than controls (0.7%),

suggesting that the development or re-suggesting that the development or re-

currence of acute psychosis in the contextcurrence of acute psychosis in the context

of cannabis use may be associated with aof cannabis use may be associated with a

genetic predisposition to schizophrenia.genetic predisposition to schizophrenia.

CANNABIS DEPENDENCECANNABIS DEPENDENCE

Evidence for cannabis dependenceEvidence for cannabis dependence

It had been believed that cannabis use didIt had been believed that cannabis use did

not lead to tolerance and that there wasnot lead to tolerance and that there was

no withdrawal syndrome. However, sinceno withdrawal syndrome. However, since

the mid-1970s, these views have beenthe mid-1970s, these views have been

challenged by many experimental andchallenged by many experimental and

observational studies. For example, Jonesobservational studies. For example, Jones

& Benowitz (1976) administered oral& Benowitz (1976) administered oral

THC in doses of 70210 mg/day to subjectsTHC in doses of 70210 mg/day to subjects

for 30 days and noted a progressive loss offor 30 days and noted a progressive loss ofthe subjective `high'. This finding was repli-the subjective `high'. This finding was repli-

cated by Georgotas & Zeidenberg (1979),cated by Georgotas & Zeidenberg (1979),

who gave an average daily dose of 210 mgwho gave an average daily dose of 210 mg

THC to volunteers for a 4-week period THC to volunteers for a 4-week period

the subjects then ``found that the marijuanathe subjects then ``found that the marijuana

was much weaker''. Withdrawal signs werewas much weaker''. Withdrawal signs were

also found: during the first week of absti-also found: during the first week of absti-

nence the subjects ``became very irritable,nence the subjects ``became very irritable,

uncooperative, resistant and at timesuncooperative, resistant and at times

hostile''; they also became hungry andhostile''; they also became hungry and

experienced insomnia. These effects wanedexperienced insomnia. These effects waned

over 3 weeks. Cessation of smoked cannabisover 3 weeks. Cessation of smoked cannabis

has also been shown to lead to withdrawalhas also been shown to lead to withdrawalsymptoms (Haneysymptoms (Haney et al et al , 1999). The, 1999). The

cannabis-withdrawal syndrome has nowcannabis-withdrawal syndrome has now

been unequivocally demonstrated and in-been unequivocally demonstrated and in-

cludes restlessness, anxiety, dysphoria,cludes restlessness, anxiety, dysphoria,

irritability, insomnia, anorexia, muscleirritability, insomnia, anorexia, muscle

tremor, increased reflexes and autonomictremor, increased reflexes and autonomic

effects including changes in heart rate,effects including changes in heart rate,

blood pressure, sweating and diarrhoea.blood pressure, sweating and diarrhoea.The syndrome may appear in about 10The syndrome may appear in about 10

hours, and peaks at about 48 hourshours, and peaks at about 48 hours

(Mendelson(Mendelson et alet al, 1984)., 1984).

The validity of cannabisThe validity of cannabis

dependencedependence

TheThe Diagnostic and Statistical Manual ofDiagnostic and Statistical Manual of

Mental DisordersMental Disorders (DSMIV; American(DSMIV; American

Psychiatric Association, 1994) presentsPsychiatric Association, 1994) presents

criteria for the diagnosis of psychoactivecriteria for the diagnosis of psychoactive

substance dependence, based largely onsubstance dependence, based largely on

the concept of the dependence syndromethe concept of the dependence syndrome

(Edwards(Edwards et alet al, 1981). The key features of, 1981). The key features of

DSMIV substance dependence are cogni-DSMIV substance dependence are cogni-

tive, behavioural and physiological symp-tive, behavioural and physiological symp-

toms, indicating that the individualtoms, indicating that the individual

continues to use the substance despite signi-continues to use the substance despite signi-

ficant substance-related problems. Theficant substance-related problems. The

criteria include tolerance, a withdrawalcriteria include tolerance, a withdrawal

syndrome, difficulty in controlling con-syndrome, difficulty in controlling con-

sumption and a pattern of use which leadssumption and a pattern of use which leads

to a reduction in other important activities.to a reduction in other important activities.

In an empirical study, MorgensternIn an empirical study, Morgenstern et alet al

(1994) found the DSM concept of cannabis(1994) found the DSM concept of cannabis

dependence as least as valid as those fordependence as least as valid as those for

dependence on alcohol, opiates, stimulantsdependence on alcohol, opiates, stimulants

and sedatives.and sedatives.

Prevalence and course of cannabisPrevalence and course of cannabis

dependencedependence

From ECA data, Anthony & Helzer (1991)From ECA data, Anthony & Helzer (1991)

showed that men had a higher prevalenceshowed that men had a higher prevalence

(7.7%) of cannabis abuse or dependence(7.7%) of cannabis abuse or dependence

than women (4.8%). This was largely duethan women (4.8%). This was largely due

to the greater exposure to illicit drugs ofto the greater exposure to illicit drugs of

men, since the prevalence of a diagnosis ofmen, since the prevalence of a diagnosis of

abuse/dependence among those who hadabuse/dependence among those who had

used cannabis more than five times wasused cannabis more than five times wasthe same in men and women (21% andthe same in men and women (21% and

19%, respectively). Extrapolating from19%, respectively). Extrapolating from

these data, Hallthese data, Hall et alet al (1994) suggest that(1994) suggest that

about 17% of those who used cannabisabout 17% of those who used cannabis

more than five times would meet DSMIIImore than five times would meet DSMIII

criteria for dependence, and that for thosecriteria for dependence, and that for those

who have ever used there is approximatelywho have ever used there is approximately

a 1/10 risk.a 1/10 risk.

From a New Zealand birth cohort ofFrom a New Zealand birth cohort of

1265 children, Fergusson & Horwood1265 children, Fergusson & Horwood

(2000) found that by the age of 21, nearly(2000) found that by the age of 21, nearly

70% had used cannabis and over 9% met70% had used cannabis and over 9% met

DSMIV criteria for cannabis dependence.DSMIV criteria for cannabis dependence.Key predictors were male gender, ethnicKey predictors were male gender, ethnic

11 911 9


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JOHNSJOHNS

minorityminority status and measures of adoles-status and measures of adoles-

cent risk-cent risk-taking behaviours, includingtaking behaviours, including

cigarette smoking, conduct problems andcigarette smoking, conduct problems and

a delinquent peer group.a delinquent peer group.

WiesbeckWiesbeck et alet al (1996) set out to deter-(1996) set out to deter-

minemine the prevalence of the cannabis-the prevalence of the cannabis-

withdrawal syndrome in people who hadwithdrawal syndrome in people who hadused the drug but who were not in treat-used the drug but who were not in treat-

ment. In a cohort of 5611 individuals,ment. In a cohort of 5611 individuals,

31% had taken the drug on more than 2131% had taken the drug on more than 21

occasions in a year. Among these moreoccasions in a year. Among these more

frequent users, 16% met criteria for afrequent users, 16% met criteria for a

cannabis-withdrawal syndrome i.e. atcannabis-withdrawal syndrome i.e. at

least any one of the following: feelingleast any one of the following: feeling

nervous or irritable, insomnia, tremor,nervous or irritable, insomnia, tremor,

sweats, nausea, gastrointestinal disturbancesweats, nausea, gastrointestinal disturbance

or appetite change. These individuals hador appetite change. These individuals had

used the drug almost daily for an averageused the drug almost daily for an average

of 70 months and even when use of alcoholof 70 months and even when use of alcohol

and other drugs was considered, cannabisand other drugs was considered, cannabisuse was still significantly related to a self-use was still significantly related to a self-

report of a history of cannabis withdrawal.report of a history of cannabis withdrawal.

Thomas (1996) found that 35% ofThomas (1996) found that 35% of

cannabis users said that they could not stopcannabis users said that they could not stop

when they wanted to, 24% continued towhen they wanted to, 24% continued to

use despite problems attributed to the druguse despite problems attributed to the drug

and 13% felt that they could not controland 13% felt that they could not control

their consumption. Restlessness or irrit-their consumption. Restlessness or irrit-

ability if they could not use cannabis wasability if they could not use cannabis was

reported by 20% of those surveyed.reported by 20% of those surveyed.

Interestingly, dependent users were no moreInterestingly, dependent users were no more

likely to report panic or psychotic episodeslikely to report panic or psychotic episodes

than those classed as non-dependent. Withthan those classed as non-dependent. Withregard to untoward social consequences,regard to untoward social consequences,

14% of cannabis users agreed that the con-14% of cannabis users agreed that the con-

sumption of the drug had caused them tosumption of the drug had caused them to

neglect activities previously consideredneglect activities previously considered

important or enjoyable. These findingsimportant or enjoyable. These findings

(Thomas, 1996) have to be qualified by the(Thomas, 1996) have to be qualified by the

low overall response rate of 35%, the uselow overall response rate of 35%, the use

of unvalidated criteria for cannabisof unvalidated criteria for cannabis

dependence and by the lack of data ondependence and by the lack of data on

misuse of alcohol or other drugs among themisuse of alcohol or other drugs among the

sample.sample.

SwiftSwift et alet al (1998) interviewed a sample(1998) interviewed a sample

from New South Wales of 243 long-termfrom New South Wales of 243 long-termcannabis users who were smoking 34cannabis users who were smoking 34

times a week. A lifetime prevalence oftimes a week. A lifetime prevalence of

57% was found for both DSMIIIR and57% was found for both DSMIIIR and

ICD10 (World Health Organization,ICD10 (World Health Organization,

1992) dependence, but only a quarter per-1992) dependence, but only a quarter per-

ceived that they had a cannabis problem.ceived that they had a cannabis problem.

VULNERABILITYVULNERABILITY

TO ADVERSE EFFECTSTO ADVERSE EFFECTS

OF CANNABISOF CANNABIS

It has previously been emphasised thatIt has previously been emphasised thatconstitutional factors such as relativeconstitutional factors such as relative

youthfulness, personality and misuse ofyouthfulness, personality and misuse of

other drugs, may act as vulnerability factorsother drugs, may act as vulnerability factors

to the adverse mental effects of cannabis.to the adverse mental effects of cannabis.

Mental illness as a vulnerability factor hasMental illness as a vulnerability factor has

been reviewed in the previous section.been reviewed in the previous section.

AdolescenceAdolescence

There are a number of reasons why adoles-There are a number of reasons why adoles-

cence may be regarded as a time of vulner-cence may be regarded as a time of vulner-

ability for the adverse mental effects ofability for the adverse mental effects of

cannabis. First, adolescents may experiencecannabis. First, adolescents may experience

emotional problems that cue cannabis use,emotional problems that cue cannabis use,

and their relative youth may lead to anand their relative youth may lead to an

increased risk of adverse mental states onincreased risk of adverse mental states on

using the drug. Second, regular use ofusing the drug. Second, regular use of

cannabis may interfere with learning andcannabis may interfere with learning and

personal development. Last, early initiationpersonal development. Last, early initiation

of cannabis use may predict an increasedof cannabis use may predict an increased

risk of escalation in risk and progressionrisk of escalation in risk and progression

to other drugs.to other drugs.

With regard to the possible impact ofWith regard to the possible impact of

emotional problems, Newcombe & Bentleremotional problems, Newcombe & Bentler

(1988) found a strong relationship between(1988) found a strong relationship between

adolescent drug use and the experience ofadolescent drug use and the experience of

emotional distress, depression and lack ofemotional distress, depression and lack of

a sense of purpose in life. As to the prospecta sense of purpose in life. As to the prospect

of adverse mental states on using high dosesof adverse mental states on using high doses

of cannabis, this review has demonstratedof cannabis, this review has demonstrated

dose-related effects in adults and thedose-related effects in adults and the

younger user is not likely to be at any lesseryounger user is not likely to be at any lesser

risk. Crowleyrisk. Crowley et alet al (1998) found that for(1998) found that for

adolescents with conduct problems, canna-adolescents with conduct problems, canna-

bis use was not benign in that misuse wasbis use was not benign in that misuse was

associated with high rates of dependenceassociated with high rates of dependence

and withdrawal.and withdrawal.

The possible effects of cannabis con-The possible effects of cannabis con-

sumption on the educational performancesumption on the educational performance

of adolescents are not easy to demonstrateof adolescents are not easy to demonstrate

in population studies (Hallin population studies (Hall et alet al, 1994)., 1994).

Newcombe & Bentler (1988), having con-Newcombe & Bentler (1988), having con-

trolled for the higher nonconformity andtrolled for the higher nonconformity and

the lower academic potential amongthe lower academic potential among

adolescent drug users, found only a modestadolescent drug users, found only a modest

negative link between drug use and collegenegative link between drug use and college

involvement. Schwartzinvolvement. Schwartz et alet al (1989) found(1989) foundshort-term memory impairment in 10short-term memory impairment in 10

cannabis-dependent adolescents comparedcannabis-dependent adolescents compared

with matched controls. Test results tendedwith matched controls. Test results tended

to improve over 6 weeks, which suggestedto improve over 6 weeks, which suggested

that the deficits observed were due to pastthat the deficits observed were due to past

cannabis use.cannabis use.

Polydrug usePolydrug use

A substantial number of young people inA substantial number of young people in

the community use a range of drugs whichthe community use a range of drugs which

includes cannabis. Ramsay & Percyincludes cannabis. Ramsay & Percy

(1996) found that 4% of a group of 16-(1996) found that 4% of a group of 16-

to 29-year-olds admitted using cannabisto 29-year-olds admitted using cannabisand other drugs in the past month, byand other drugs in the past month, by

contrast with 8% who had used only can-contrast with 8% who had used only can-

nabis. Clinical observation suggests thatnabis. Clinical observation suggests that

cannabis users who also misuse other drugscannabis users who also misuse other drugs

or alcohol seem to experience more severeor alcohol seem to experience more severe

mental health problems than those whomental health problems than those who

solely take cannabis, but there do notsolely take cannabis, but there do not

appear to be any substantial publishedappear to be any substantial publishedstudies on this issue. Polydrug use is astudies on this issue. Polydrug use is a

recognised concern in psychiatric popula-recognised concern in psychiatric popula-

tions: for example, Baigenttions: for example, Baigent et alet al (1995)(1995)

found that 20% of their dual-diagnosisfound that 20% of their dual-diagnosis

#patients misused more than one substance.#patients misused more than one substance.

PersonalityPersonality

Given the heterogeneity of the populationGiven the heterogeneity of the population

of cannabis users, it is not surprising thatof cannabis users, it is not surprising that

no single personality type or disorder isno single personality type or disorder is

particular to users of that drug or, indeed,particular to users of that drug or, indeed,

to users of any illicit drug (Allen & Frances,to users of any illicit drug (Allen & Frances,

1986). However, it is a matter of clinical1986). However, it is a matter of clinical

observation that the use of cannabis byobservation that the use of cannabis by

some individuals seems to be predisposedsome individuals seems to be predisposed

by traits such as social anxiety, anxiety orby traits such as social anxiety, anxiety or

dysphoria. Such posited use as a form ofdysphoria. Such posited use as a form of

self-medication to relieve unwanted affectsself-medication to relieve unwanted affects

or feelings was not corroborated in a studyor feelings was not corroborated in a study

of cannabis-dependent individuals (Greeneof cannabis-dependent individuals (Greene

et alet al, 1993). There is good evidence for, 1993). There is good evidence for

the comorbidity of drug misuse and somethe comorbidity of drug misuse and some

personality disorders. For example, Regierpersonality disorders. For example, Regier

et alet al (1990) report that some form of(1990) report that some form of

substance abuse was identified in 83.6%substance abuse was identified in 83.6%

of individuals with antisocial personalityof individuals with antisocial personality

disorder (ASPD), with an odds ratio ofdisorder (ASPD), with an odds ratio of

29.6. It should be appreciated that this very29.6. It should be appreciated that this very

high rate arises because substance abuse ishigh rate arises because substance abuse is

one of the major diagnostic criteria forone of the major diagnostic criteria for

ASPD; only 16% of individuals with ASPDASPD; only 16% of individuals with ASPD

did not have a history of substance abuse.did not have a history of substance abuse.

The same study showed that the lifetimeThe same study showed that the lifetime

prevalence of ASPD in cannabis abuse orprevalence of ASPD in cannabis abuse or

dependence was 14.7% with an odds ratiodependence was 14.7% with an odds ratio

of 8.3. The interaction between ASPD andof 8.3. The interaction between ASPD and

cannabis use is too complex to explore atcannabis use is too complex to explore at

length in this review, but it is probable thatlength in this review, but it is probable thateach disorder exacerbates the adverseeach disorder exacerbates the adverse

effects of the other. See Dolan & Coideffects of the other. See Dolan & Coid

(1993) for a discussion of factors determin-(1993) for a discussion of factors determin-

ing outcome in ASPD.ing outcome in ASPD.

Implications for mental health careImplications for mental health care

How should mental health services respondHow should mental health services respond

to these findings? The key priorities are: (a)to these findings? The key priorities are: (a)

risk-management and care-planning haverisk-management and care-planning have

to be informed by a thorough substance-to be informed by a thorough substance-

misuse assessment (Johns, 1997); (b) com-misuse assessment (Johns, 1997); (b) com-

munity and in-patient psychiatric servicesmunity and in-patient psychiatric services

should develop policies on substance useshould develop policies on substance usewhich balance the treatment needs ofwhich balance the treatment needs of

1 2 01 2 0


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individual patients with duties of care toindividual patients with duties of care to

other patients and to the general public;other patients and to the general public;

and (c) research is needed into treatment in-and (c) research is needed into treatment in-

terventions for patients with mental illnessterventions for patients with mental illness

and substance misuse problems.and substance misuse problems.

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12 11 21

CLINICAL IMPLICATIONSCLINICAL IMPLICATIONS

&& Among those who have ever taken cannabis,1/10 are at riskof dependence.Among those who have ever taken cannabis,1/10 are at risk of dependence.

&& Heavy cannabis misuse leads to the risk of psychotic episodes, and aggravates theHeavy cannabis misuse leads to the risk of psychotic episodes, and aggravates the

symptoms and course of schizophrenia.symptoms and course of schizophrenia.

&& For any psychiatric patient, risk-management and care-planning is incompleteFor any psychiatric patient, risk-management and care-planning is incomplete

without a thorough assessment of substance misuse.without a thorough a ssessment of substance misuse.

LIMITATIONSLIMITATIONS

&& The available literature shows a preponderance of case reports and uncontrolledThe available literature shows a preponderance of case reports and uncontrolled

studies.studies.

&& Epidemiological findings from one setting cannot be assumed to generalise toEpidemiological findings from one setting cannot be assumed to generalise to

other cultural groups.other cultural groups.

&& It is not easy to determine causal explanations from the studies cited.It is not easy to determine causal explanations from the studies cited.

ANDREW JOHNS, FRCPsych, Depar tment of Forensic Psychiatry, Institute of Psychiatry, De Crespigny Park,ANDREW JOHNS, FRCPsych, Department of Forensic Psychiatry, Institute of Psychiatry, De Crespigny Park,

Denmark Hill,London SE5 8 AF. Tel: 020 7919 3123Denmark Hill, London SE5 8 AF. Tel: 02 0 7 919 3123

(First received 22 July 1999, final revision 4 September 200 0, accepted 6 September 20 00)(First received 22 July 1999, final revision 4 September 200 0, accepted 6 September 20 00)


8/8

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