Substance misuse and violence: acomparison of special hospitalinpatients diagnosed with eitherschizophrenia or personality disorder

MARK CORBETT Research Worker, Rampton Hospital Authority, Retford,Nottinghamshire, DN22 0PD, UK

CONOR DUGGAN Professor, Division of Forensic Mental Health,University of Leicester, Leicester LE5 OLE, UK

EMMET LARKIN Forensic Psychiatrist and Clinical Director, Arnold LodgeRSU, Cordelia Close, Leicester LE5 0LE, UK

ABSTRACT: There is increasing interest in the relationship between schizophrenia,substance misuse and serious violence. We compared the pattern of substance misusein inpatients with schizophrenia convicted of serious offences with that of a matchedgroup with personality disorder. We also compared those with and without a history ofsubstance misuse in their use of drugs or alcohol at the time of their violent indexoffence. We matched 75 substance misusing patients with schizophrenia with a groupof patients with personality disorder and compared the types of substances misused inboth groups. We compared these two groups with a larger sample of inpatients withouta history of substance misuse to determine the presence of substance misuse at thetime of the index offence. No differences were found between the matched groups intheir choice of drugs. Drug abusing male inpatients with a personality disorder weresignificantly more likely to have consumed alcohol at the time of the violent offencecompared with the other groups. Although the reporting of substance misuse wasunexpectedly low, our data (a) showed no evidence that patients with schizophreniapreferentially choose to misuse specific types of drugs compared with personality disor-dered patients and (b) that intoxication with alcohol at the time of the violent offencemay be important in male patients with a personality disorder and a history of sub-stance misuse.

Introduction

The established link between schizophrenia, substance misuse and violencesuggests that this will be an increasingly important area for mental healthworkers. Although schizophrenia has only a modest association with violenceoverall (Wessley et al., 1994), it is over-associated with serious violence espe-cially in the presence of substance misuse (Swanson et al., 1990; Swanson,1994; Dyer, 1996). Apart from its clinical importance in increasing the risk of

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violence, there is the additional question about whether these patients chooseto misuse certain substances over others. This selective matching of specificsubstances (and their subjective effects) with specific symptoms might suggestthat substance misuse in schizophrenia is an attempt at self-medication(Dixon et al., 1991) and might also illuminate the neurochemical basis ofschizophrenia (McLellan and Druley, 1977).

The previous studies on whether there is a relationship between schizo-phrenia and a specific pattern of substance misuse have shown inconsistentfindings. Schneier and Siris (1987) in a review, concluded that a strikinglynon-random distribution of substance misuse existed with schizophrenicgroups using more amphetamines, cocaine, cannabis, hallucinogens,inhalants, tobacco and caffeine, and less alcohol, opiates and sedative hypnotics than control populations (of varying composition). Although thissupports a selective matching by diagnosis, few of the studies in this reviewcontrolled for social and demographic factors which might, independent ofdiagnosis, correlate with the choice of substances misused. It is no surprisetherefore that several other studies (for instance, Mueser et al., 1990, 1992;El-Guebaly and Hodgins, 1992; Cuffel et al., 1993; Baigent et al., 1995) con-clude that price, availability, and demographic characteristics (such as sex, ageand socioeconomic status) are strong predictors of type of substance abuse andthat diagnoses have little, if any, influence. However, these studies again didnot involve pairing patients with schizophrenia with controls of a differentpsychiatric diagnosis. Since the pattern of substance misuse has changed radi-cally over the past 20 years (Pope et al., 1990), such matching between thepatients with schizophrenia and the control population is essential to ensurethat like is compared with like.

Another important question is whether a history of substance misusemakes it more likely that such substances are used at the time of a violentoffence and therefore that this might increase the risk of such offending.Common sense would suggest that this be the case but we need to establishthis association.

Our study had two aims: (a) to investigate whether patients detained inhigh security with schizophrenia selectively misuse certain substances com-pared with a matched sample of patients with personality disorder and (b) todetermine the importance of substance misuse at the time of the violent indexoffence in those with and without a history of long-term drug misuse.

Method

The sample

The study sample was selected from psychiatric patients admitted tothree English high security (special) hospitals (Ashworth, Broadmoor orRampton) between 1972 and 1995. All the patients within special hospitals

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are compulsorily detained and the majority have been convicted of violentoffences. Data were obtained from the Special Hospitals’ Case Register whichis a database of information obtained from standardized structured interviewswith patients on admission in addition to data gathered from the patient’smedical history file, medical records, criminal records and police reports. Togain entry into the study, the patient had to have a sole diagnosis by theresponsible medical officer (RMO) of either schizophrenia or of personalitydisorder and to have admitted to substance misuse (see below). We includedonly Caucasians, thereby avoiding the controversy surrounding diagnosis ofschizophrenia in Afro-Caribbeans (Littlewood and Lipsedge, 1981), whilealso excluding the need to match patients for ethnicity. In addition to thisprimary comparison, we also selected two comparison groups, again allCaucasian, one with a diagnosis of schizophrenia and the other with a diag-nosis of personality disorder, who had also been convicted of violent indexoffences but who did not admit to a history of substance misuse.

Drug misuse

As part of the initial case register interview, details of illicit drug use duringthe year before admission were requested and are coded as follows:

(i) those who have taken the drug on one occasion or on very few occasionsonly;

(ii) those who have taken the drug intermittently (e.g. at weekends over atleast three months);

(iii) those who have taken the drug regularly (daily or several times a weekover several months or longer);

(iv) those who consider themselves as addicted or who have a history of atten-dance at a drug treatment unit.

Amphetamines, barbiturates, cannabis, LSD and opiates are all coded in thisway. Only patients coded as level (ii), (iii) or (iv), for at least one of thesesubstances, were eligible for inclusion in this study. The study is thereforeconcerned with whether or not a patient admitted to the regular use of a par-ticular substance and not necessarily whether or not they were classed as sub-stance abusers. We also classed as positive those patients who admitted todrinking four units of alcohol, or more, per day. Information on drug or alco-hol use at the time of the index offence was also recorded separately on theSpecial Hospitals’ Case Register.

Matching

To control for different patterns of drug use over time, between age groups,and between social classes, patients were matched for decade of birth, age on

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314 Corbett et al.

admission (five-year intervals, i.e. 15–20, 20–25, etc.) and social class (classi-fied according to the Office of Population Censuses and Surveys’ Classificationof Occupations publication). Patients were also to be paired for sex but, of the111 patients with schizophrenia who satisfied the inclusion criteria, only three(3%) were female compared with 45 out of 160 (28%) for the personality dis-order group. The pairing was therefore confined to males only, with the femalepersonality disorder group being described separately. After endeavouring tomatch the 111 patients suffering from schizophrenia with the 160 personalitydisordered patients on the three criteria, 75 pairs resulted.

Statistical analysis

McNemar’s test (with a continuity correction) was used to calculate the chi2

values for the matched samples. For those samples that were not matched, astandard chi2 (for two independent proportions) was used.

Results

Of the 1111 patients with a sole diagnosis of schizophrenia admitted to any ofthe three special hospitals between 1972 and 1995, 167 (15%) admitted toillegal substance misuse at Case Register level (ii) or above (only threepatients were classed as level (iv)). Only 3.3% of the 1111 were classified asdrug dependent and 2.3% as alcohol dependent by their RMO. There were885 patients with personality disorder of whom 158 (18%) admitted to drugmisuse. Of these 885, 4.5% and 6.4% were classified as drug or as alcoholdependent respectively by their consultant. The ages of the study cohorts wereas follows: men with schizophrenia (mean 27.6, SD 5.8, range 19.6–45.0), menwith personality disorder (mean 27.3, sd, 6.3, range, 18.6–47.0), women withpersonality disorder (mean 23.6, SD 4.4, range 17.7–40.3). Table 1 shows thepercentage of those who admitted to misusing each type of drug in the

Table 1: Details of substance misuse prevalence in the three cohorts of special hospital patientswho admitted to substance misuse during the year before admission (% in parentheses)

Personality disorder Schizophrenia Personality disorderMales (n = 75) Males (n = 75) Females (n = 45)

Amphetamines 26* (35) 21(28) 23 (51)Barbiturates 15 (20) 8 (11) 11 (24)Cannabis 67* (91) 73 (97) 35 (78)LSD 18* (24) 15 (20) 17 (38)Opiates 8 (11) 10* (14) 14 (31)Alcohol 63 (84) 62 (83) 35** (80)

Note:* n = 74; **n = 44

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matched pair of male patients and for the female patients with a personalitydisorder.

For the paired male sample the mean number of illegal substances used (aminimum of one and a maximum of five per patient) was 1.8 for the patientswith a personality disorder and 1.7 for the patients with schizophrenia (notsignificantly different when analysed using the paired t-test, assuming normaldistributions). Six patients with schizophrenia and seven patients with a per-sonality disorder were also coded as having abused another type of substancenot included in the table (e.g. ecstasy or cocaine). The mean number of illegalsubstances abused for the personality disordered females was 2.5. Table 2shows the results of the analyses examining any differences between the twomatched groups regarding choice of drug used; none of the comparisons wassignificantly different.

Criminal offences

Table 3 shows the index offences committed by the three patient groups. Wegrouped together the homicidal and violent offences and compared their fre-quency with the remainder of the offending in the two male groups usingMcNemar’s test. The schizophrenia group were significantly more likely tohave been convicted of a violent or homicidal offence compared with thepersonality disordered group (chi2=13.8, p <0.001). Conversely, those withpersonality disorder were more likely to have been convicted of a sexualoffence or arson.

Table 4 compares those in our sample with a history of substance misusewho had committed a violent or homicidal index offence with a sample of sim-ilarly diagnosed patients who had also committed a violent or homicidal indexoffence, but who had not admitted to substance misuse in the year prior toadmission to hospital. The table compares the numbers in each diagnostic cat-egory for drug or alcohol intoxication at the time of the index offence. Of the60 patients with schizophrenia and a history of substance misuse, 26 (43%) hadtaken drugs or alcohol at the time of the offence (five taking both). Of the 36patients with personality disorder, a history of substance misuse and a homici-dal or violent offence, 23 (64%) had taken drugs or alcohol at the time of theoffence (with again five taking both). For the two groups with a history of sub-stance misuse, the patients with a personality disorder were significantly morelikely to have consumed alcohol at the time of the offence compared with thepatients with schizophrenia (chi2=9.1, p <0.003). When the rates of substancemisuse in these two groups are compared with similarly diagnosed patients witha violent offence but without a reported history of substance misuse, both theformer groups as expected were more likely to have taken illegal drugs at thetime of the offence (27% versus 5% for those with schizophrenia and 22% ver-sus 3% for the personality disordered). For alcohol, however, the pattern wasdifferent: patients with personality disorder and a history of substance misuse

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316 Corbett et al.

Tab

le 2

: Com

pari

son

of m

isus

e of

sub

stan

ces

in t

he y

ear

befo

re a

dmis

sion

am

ong

a sa

mpl

e of

mat

ched

fore

nsic

psy

chia

tric

inpa

tien

ts w

ith

schi

zoph

reni

a or

a pe

rson

alit

y di

sord

er

Subs

tanc

eT

otal

no.

of

Bot

h pa

tien

ts

Nei

ther

pat

ient

One

pat

ient

M

cNem

ar te

st

Sign

igic

ant a

t 10%

pair

s mat

ched

took

dru

g Y

/Yto

ok d

rug

N/N

took

dru

gχ2

valu

ele

vel?

(T

wo

taile

d)

Schi

z = y

esSc

hiz =

no

PD =

no

PD =

yes

Am

phet

amin

es74

*7

3513

190.

78N

oB

arbi

tura

tes

752

546

131.

89N

oC

anna

bis

74*

650

72

1.77

No

LSD

74*

647

912

0.19

No

Opi

ates

74*

157

97

0.06

No

Alc

ohol

7552

210

11ze

roN

o

Not

e: *

One

pai

r om

itte

d be

caus

e th

e su

bsta

nce

use

for t

hese

subs

tanc

es w

as n

ot k

now

n fo

r one

mem

ber o

f a p

air

CBMH 8(4)2nd/JH copy 15/12/05 9:42 am Page 316

were twice as likely as the two comparison groups to have taken alcohol at thetime of the index offence. Conversely, patients with schizophrenia and a histo-ry of substance misuse were no more likely than the two comparison groups tohave taken alcohol at the time of the violent offence.

Discussion

There were three main findings from this study. First, we failed to establishthat patients with schizophrenia detained in a special hospital had a differentpattern in their choice of illicit drugs compared with similarly detained

Table 4: Comparison of sample groups of special hospital patients for whether drugs oralcohol were taken shortly before the index offence (violent and homicide offences only)(% in parentheses)

Personality Schizophrenic, Personality Schizophrenic,disordered, history of illegal disordered, no history

history substance misuse no history of illegal of illegal of illegal substance misuse

substance misuse substance misuse

n 36* 60 273 for alcohol 356 for alcohol**244 for drugs **360 for drugs

Took alcohol 20 (56) 15 (25) 74 (27) 70 (20)Took illegalsubstances 8 (22) 16 (27) 7 (3) 17 (5)

Notes:*Details of drugs/alcohol relating to the offence were not known for four of the 40violent/homicide patients with a personality disorder ** The sample sizes for drugs and alcohol at the time of offence are different because forsome patients only partial information was available, e.g. it was known that a patient wasdefinitely under the influence of alcohol but the presence of drugs was coded ‘not known’.

Table 3: Index offences committed by special hospital patients with substance misuse histo-ries in the year before admission (% in parentheses)

Type of offence Personality disorder Schizophrenia Personality(m) (m) disorder (f)

Homicide 21 (28) 40 (53) 3 (7)Violence 19 (25) 20 (27) 10 (22)Threat of murder 2 (3) 1 (1) 0 (0)Sexual 14 (19) 1 (1) 1 (2)Arson 10 (13) 3 (4) 19 (42)Robbery 1 (1) 8 (11) 2 (4)Other 7 (9) 1 (1) 6 (13)No Offence 1 (1) 1 (1) 4 (9)Total 75 75 45

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patients with personality disorder. That is, we did not find a selective associa-tion of certain illicit drugs with diagnosis. Second, we found that patientswith a history of substance misuse were significantly more likely to take illegaldrugs at the time of their violent index offence compared with violent offend-ers with the same diagnosis but without a history of drug abuse. Third, wefound that the personality-disordered men who also admitted to a history ofsubstance misuse were twice as likely as the comparison groups to take alcoholat the time of the violent offence.

We found no significant differences between matched groups of drug abus-ing patients with schizophrenia or a personality disorder on examining thepattern of substance misuse. These findings support the belief of Mueser et al.(1992) that it is the availability of illicit drugs which is the important deter-minant of who abuses which substance, irrespective of its psychoactive effects,and that the prevalence of substance abuse in an individual’s social environ-ment, including their ethnic and peer group, influences the availability of dif-ferent drugs, and hence the likelihood that they will be abused. Hence thefailure to control for such variables as age, socioeconomic factors, sex and eth-nicity may explain the differences found between the drug habits of patientswith schizophrenia and the comparison groups found in previous studies.

Our data show that patients with schizophrenia do not use a specific groupof drugs as compared with a matched group of personality disordered patients.Cuffel et al. (1993), in another study which again did not support a specificpattern of drug misuse, observed that while certain demographic variables(ethnicity, socioeconomic status and marital status) were not associated withgreater risk for substance abuse in those with schizophrenia, other demograph-ic factors (such as being young and a male) were, as well as the co-occurrenceof depression. They conjectured that drug misuse in schizophrenia wasinvolved with the general effect of relieving boredom, depression and anxiety,and also to facilitate social contact.

Our second finding that those with a history of substance abuse are alsomore likely to take drugs at the time of the violent index offence is notsurprising but nevertheless is clinically important. These data have greatervalidity in that there was independent evidence from the depositions of themental state of the offender at the time of the index offence and hence thesource was not merely the individual’s own self-report which is prone tounder-reporting and comprised much of the data for the Case Register. In thecomparison between those with and without a history of substance misuse, wefound that the former were five times (for those with schizophrenia) andseven times (for those with personality disorder) more likely to have takendrugs at the time of the violent index offence.

Alcoholism has a significant association with violent offending (Hodge,1993). For example, Thomas and McMurran (1993) studied a sample of patientsat Rampton Hospital and found that, among those who had committed homi-cide, there was a disproportionate number of patients with a history of high

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alcohol consumption. Our third finding also supports this association with atleast a fifth of the patients taking alcohol at the time of the violent offence.However, this use of alcohol was especially prominent (56%) in the personality-disordered male patients who also admitted to a history of substance misuse. Incontrast, patients with schizophrenia and a history of substance misuse had thesame level of alcohol intoxication as the two control non-substance-misusingcomparison groups. Again, we believe that this may be important clinically inthat future violent behaviour in personality-disordered individuals (as comparedwith those with schizophrenia) is very difficult to predict. This finding requiresreplication but suggests that the combination of illicit drugs, alcoholic intoxica-tion and personality disorder in males may be an important predictor of futureviolent behaviour. Hence, these results may be important for both risk manage-ment and the targeting of therapeutic intervention.

This study had limitations. First, the study considered special hospitalpatients only and this severely limits the generalizability of the results.Second, the retrospective nature of the study severely restricted the nature ofthe inquiry. For instance, data on the use of cocaine were not collected andtherefore we did not include this commonly misused drug in the analysis.Third, it was not possible to examine many female patients with a history ofsubstance misuse and schizophrenia which may be a reflection of the lesssevere course in female patients with schizophrenia (Goldstein, 1988). Fourth,patients with a dual diagnosis of schizophrenia and substance misuse may bemisdiagnosed as having schizophrenia when the features of psychosis may bedrug induced. However, we believe that this is unlikely in this setting as thepatients had usually been ill for some time and further substance misuse with-in a special hospital is most unlikely, therefore we would argue that this is atrue co-morbidity of schizophrenia and substance misuse.

A more significant limitation, given the reported frequent co-occurrence ofmental disorder with substance misuse, was that such a co-occurrence in thissample was relatively uncommon. This low rate of substance misuse in thementally disordered in special hospitals has also been reported recently in amore systematic record survey of all patients resident in special hospitals over asix-month period (Taylor et al., 1998). They found rates of substance misuse of7.5% in those with schizophrenia alone and 14% in those with personality dis-order alone. The comparable figures in our study were 15% and 18% respec-tively. There are a number of non-mutually exclusive explanations for theselow rates. First, the presence of substance misuse may not be adequatelyinquired about or documented. Second, patients are known to under-reporttheir level of substance misuse (Test et al., 1989) and may be especially likelyto do so when being compulsorily detained. Third, the presence of co-morbidsubstance misuse may be a barrier to being admitted to a special hospital.Fourth, as Taylor et al. (1998) point out, patients admitted to a special hospitalgenerally have long durations of admission, hence data on current inpatientsmay reflect a pattern of behaviour which was prevalent several years previously

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when substance misuse was much less common. Without more data, it is notpossible to judge which of these is the correct explanation; however, for thisstudy under-reporting is not such a problem provided that there was not a sys-tematic bias in the under-reporting of either group and we have no reason tobelieve that this was the case. Set against these limitations, our study had theadvantage over many previous investigations in that it contained a relativelylarge sample which we matched by factors which might affect substance misuse(e.g. decade of birth etc.).

In conclusion, we have established that while patients with schizophreniado not have a specific pattern of drug misuse, patients with either schizophre-nia or personality disorder who have a history of substance misuse are signifi-cantly more likely to use illicit drugs at the time of a violent offence comparedwith similarly diagnosed patients without such a history. We have also shownthat alcohol was a frequent accompaniment in violent offending in all thegroups studied but that it was especially common in male patients with a his-tory of substance misuse and personality disorder. From these data, we canonly conjecture about the role of substance misuse in the offending behaviourbut it is clear that this is common in those who commit violent offences. Asthere is now an imperative to estimate the risk of future violence among thementally disordered, these data provide additional empirical support for theimportance of eliciting a history of substance misuse for both satisfactory riskmanagement and the better targeting of our therapeutic effort (Johns, 1997).

Acknowledgement

The authors would like to thank Mrs Rita Dacey for her assistance in provid-ing data from the Special Hospitals’ Case Register. The authors would alsolike to thank Professor Pamela Taylor and Doctor Andrew Johns for theirhelpful comments on an earlier draft of this manuscript.

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