Post on 30-Dec-2015
description
Reducing the Harms of Cannabis Use:
The Policy Debate in Australia
Wayne Hall
National Drug and Alcohol
Research Centre
Outline
Analysis of harms caused by cannabis use– to cannabis users and others
Analysis of harms arising from prohibition– to cannabis users and others– using Australian data
Proposals for reducing both sets of harms– under discussion in Australia
Some tentative policy prophecies
Cannabis use among Australian males, 1998 NDS Survey
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ever usedused past yearpast week
Cannabis use among Australian females, 1998 NDS Survey
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14-19 20-29 30-39 40-49 50-59 60+
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ever usedused past yearpast week
Difficulties in Assessing the Adverse Health Effects of Cannabis Use
Limited evidence base– rigour vs relevance of animal studies
– paucity of epidemiological research
– problems in causal inference• other drug use• user characteristics
Social context of the evaluation– polarised views
– problem deflation and inflation
Acute Health Effects
anxiety, dysphoria, panic, paranoia– especially among naive users
cognitive and psychomotor impairment while intoxicated
psychotic symptoms (probably rare)– high doses of THC– vulnerability
Accidental Injury
Impaired performance on complex tasks Reduced risk taking
– aware of impairment
Simulated driving impaired Epidemiological evidence unclear
– measurement of impairment– confounding with alcohol
Health Effects of Chronic Use
Respiratory disease Dependence Effects of Maternal cannabis use Effects on adolescent development Schizophrenia & psychosis Issue of increased THC content
Respiratory Effects
Cannabis primarily smoked Cannabis smoke similar to tobacco smoke Tobacco smoking causes
– obstructive respiratory disease– respiratory infections– lung cancer
Most also smoke tobacco
Evidence
Increased cough, sputum, wheeze Histopathological changes
– most marked in MT– at an earlier age
Impaired immunological responses– pulmonary alveolar macrophages
Increased health service use Decreased respiratory function ?
Respiratory Cancers
Cause for concern– composition of cannabis smoke– histopathological changes– case series of cancers in young adults– evidence of mutational changes in lung tissue
Case-control studies a priority
Public Health Impact of Respiratory Risks
small by comparison with tobacco– in public health terms– not in terms of personal risk
a consequence of smoking as a route – encouraging non-smoking use?
most smoke tobacco anyway– amplification of respiratory risks
Significance of a Dependence Syndrome
Thought to have a low dependence potential – apparent absence of a withdrawal syndrome
Important for informed choice by users– users need to be aware of the risk
Increases exposure to health risks– by increasing duration of use
Evidence
Users seeking help to stop– Australia, Sweden, & USA
Epidemiological studies– ECA 4% population lifetime– NCS 4% population lifetime– NSMWHB 2% of population past year
Tolerance and withdrawal
tolerance in animal & human studies withdrawal syndrome in animals
– elicited by cannabinoid antagonist
withdrawal symptoms in human laboratory studies:– irritability, anxiety, insomnia, depression
these common in clinical populations
Clinical features
a withdrawal syndrome common in users seeking help
compulsive use patterns– also common in problem users
perceived to be a problem?– by a minority who meet criteria in community– as for alcohol & other drugs
Risks and Consequences
Risks– 9% of lifetime users (NCS study)– 33-50% of daily users
Consequences?– respiratory symptoms– impaired memory– poor work performance– social disapproval
Need for Treatment
Fewer than 10% seek any treatment Why so few?
– high rates of remission?– fewer consequences?– existing treatment services unattractive?
How treatable?– self-help– brief interventions– psychotherapy
Adolescent Development
Concerns– educational performance– progression to “harder” drugs
Issues– rarity of heavy use– causal attribution
• other drug use
• user characteristics
Natural history of cannabis useunder prohibition
initiation in mid teens most use intermittent
– relatively low capture rate for daily use
discontinue mid to late 20s– impact of marriage, mortgages & children
persistent use relatively rare– predicted by early initiation
– heavier use
Current monthly use of various drugs by age (Chen & Kandel, 1995)
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prescribed psychoactives
Educational Performance
Cross sectional studies Longitudinal studies US & NZ
– selective recruitment to use – peer influence– small direct contribution
Educational implications– exculpation & blame– school policies
A Gateway Drug?
Cross-sectional & longitudinal studies Sequence of drug involvement
– alcohol & tobacco precede
– cannabis which precedes
– heroin & other drugs
< 5% of cannabis users use “harder” drugs Progression predicted by:
– earlier initiation & heavier use
Explanations
selective recruitment to use– at risk & troubled youth more likely to use
peer networks – regular users affiliate with peers who use
– peer culture supportive of drug use & crime
drug markets – provide opportunities to use other illicit drugs
genetic vulnerability to drug dependence
Cannabis & Psychosis
“Cannabis psychosis”– toxic psychosis– functional psychosis
Cannabis as a risk factor for schizophrenia– precipitation– exacerbation
Potential significance
High prevalence of cannabis use – especially at period of risk for psychosis – complicates causal attribution
Additional cases of psychosis Exacerbation of psychosis Suffering of affected persons & families Costs of treating psychoses
“Cannabis Psychoses”
Conflicting opinions– clinical observations– limited case-control evidence
Probably exist but rare– either require large doses of THC– or vulnerability
Ethically difficult to reduce uncertainty
Cannabis & Schizophrenia
Cannabis & schizophrenia associated– in general & clinical populations
Cannabis use probably exacerbates disorder– reasonable prospective evidence
Possibly precipitates disorder in vulnerable– Swedish conscript study
Less likely to cause disorder de novo– no evidence of rising prevalence
The Issue of Potency
Claim THC content of cannabis x 30 times Absence of good data:
– testing not required – or done regularly
Media publicity to unusual cases– biased sampling
Changes in patterns of use– earlier initiation– heavier use of more potent forms
THC content of Marijuana 1980-98: US Potency Monitoring Project
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80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98
% T
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Changing Patterns of Cannabis Use
Most users smoke “heads”and use bongs Weekly+ use accounts 96% of market Earlier initiation of use:
– more regular use by younger users – more problem users?
More use among vulnerable groups• persons with schizophrenia
• conduct disordered adolescents
More obvious problem users
Possible Effects of Increased Potency
For naive users:– higher risk of dysphoric & psychotic symptoms
• higher rates of discontinuation?
– higher rates of accidental injury?
For regular users:– lower respiratory risk, if users titrate dose
– higher risk of dependence? • especially among adolescents
– more cognitive impairment?
Summary: adverse health effects
Dependence – 10% chance for users– 33-50% for daily users– consequences?
Respiratory disease– chronic bronchitis – cancer?
Motor vehicle accident risk?
Risks of Chronic Use
Adolescent use– selective recruitment to use– peer influences– indicator of at risk status
Psychosis– probably produces symptoms– probably exacerbates and possibly precipitates
schizophrenia in vulnerable
Overall Assessment
On current patterns of use – small to moderate public health impact – less than alcohol & tobacco – with possible exception of MVA, harms caused to
users
Do these adverse effects justify prohibition? Would relaxing prohibition increase:
– rates and duration of regular cannabis use?– rates of problems related to cannabis use?
Putative Harms Caused by Cannabis Prohibition
Loss of individual liberty to use cannabis A large scale cannabis blackmarket
– controlled by criminals– unregulated and no quality control– untaxed by government– corruption of public officials
Arms race in policing technology – helicopters and satellite surveillance– indoor hydroponic cultivation
The Harms of Prohibition:Effects on Rule of Law
Discriminatory non-enforcement of law– only 1-2% of past year users are prosecuted– more often lower SES, unemployed males
Brings law into disrepute among the young Effects on users of conviction
– stigma of criminal record– no impact on cannabis use – disproportionate penalty for self-harm
The Harms of Prohibition:Inefficient Uses of Scarce Resources
Paradox of cannabis law enforcement• most cannabis use goes undetected but
• majority of drug offences are for cannabis use
Inefficient use of scarce resources:• police and Criminal Justice System
Loss of medical uses of cannabis products • e.g. anti-nausea agent & appetite stimulant
• analgesic and antispasmodic
Options for Reducing Cannabis-related harms
Intensified enforcement of prohibition– US and Swedish models
Legalisation of cannabis use– de facto e.g. the Netherlands– or de jure
“Decriminalisation”: – prohibition with civil penalties– diversion into treatment or education
Intensification of Prohibition
American model– substantial fines and gaol sentences– workplace drug testing– school education & mass media campaigns– “zero tolerance” and strong social disapproval
Swedish model– disapproval similar to US – compulsory treatment rather than imprisonment
Problems with Intensified Enforcement
Costs of implementation• imprisonment or compulsory treatment• expanding role of government vs general retreat
Presupposes societal consensus• absent in Australia where opinion divided
Limits to effectiveness • may have decreased use in USA but rising again• may be easier to keep low as in Sweden
Backlash against prohibition?• excessive zeal in enforcement favours reformists
Cannabis Legalisation
a minority option in Australia (25%)– credibility of opponents and proponents
an irreversible step likely to increase heavy & regular use
– experience with alcohol & other drugs
contrary to international treaties – and international sentiment
Decriminalisation Pros Cons
A cautious step– easily reversed
Reduces – harms to users
– discriminatory enforcement
Better use of scarce resources
Minimal impact on use
Little or no effect on blackmarket
Inconsistent: – use not a crime
– but sale is
Symbolism– implies cannabis use is
safe & acceptable
A Choice of Evils
Insufficient data for utilitarian analysis Trading off incommensurable values:
– users’ health– social disorder and crime – civil liberties
A task for the political system – polarisation of public opinion– lack of consensus on trade-off– minimal changes to status quo most likely
Reduced Penalties for Personal Use
Removal gaol penalties for 1st offenders
– de jure recognition of practice
Cautioning and diversion as an alternative
– may increase number of users dealt with– a proportionate response to self-harm
Reduced Penalties for Personal Use
Reduce push for more radical reform– more reversible policy– consistent with international agreements
Coupled with penalties for use when driving – to address most probable adverse effect on
non-users Graduated penalties based on THC content?
A Necessary Breathing Space?
Epidemiological research on adverse effects – on adolescent development– serious long term health consequences
• cancers, respiratory disease, psychosis More credible health education
– scepticism about scares among young – parallels with the effects of alcohol & tobacco:
• respiratory risks, MVA, dependence, psychosis Better assessment of therapeutic uses
– AIDS& cancer related nausea and wasting
– neurological diseases and intractable pain