Transcript risks of cananbis use - University of Washington

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
percentage
Cannabis use among Australian
males, 1998 NDS Survey
80
70
60
50
40
30
20
10
0
ever used
used past year
past week
14-19
20-29
30-39
40-49
age group
50-59
60+
percentage
Cannabis use among Australian
females, 1998 NDS Survey
80
70
60
50
40
30
20
10
0
ever used
used past year
past week
14-19
20-29
30-39
40-49
age group
50-59
60+
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 use
under 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)
100
90
proportion
80
70
alcohol
60
cigarettes
50
cannabis
40
other illicit
30
prescribed psychoactives
20
10
0
10
12
14
16
18
20
22
age
24
26
28
30
32
34
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
5
% THC
4
3
2
1
0
80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98
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