Mayors' Conferences

 

The Health & Social Effects of Nonmedical Cannabis Use - The State of Knowledge: Knowns & Unknowns

Department of Mental Health & Substance Abuse WHO HQ Geneva

Presented by Mr Dag Rekve

What follows is a shortened version presentation of the report.

The full presentation can be downloaded here.
The report of non-medical use of cannabis is produced by the WHO and can be downloaded here








The report is about:

-          nonmedical use of cannabis, not medical use.

-          the health and social effects of cannabis use.

-          the current knowledge on a very broad impact on health; “what we know”.

-          priority areas for future research; where we lack sufficient knowledge.

The report is the outcome of two years of work and was developed by a broad range of scientists, medical doctors, experts that provided background papers in their area of expertise. An expert meeting was held to discuss and review the evidence. A smaller group drafted the report led by three main editors. The work was reviewed by external reviewers.

The report covers:

-          Cannabis substance profile and its health impact.

-          Neurobiology of cannabis use.

-          Short-term effects of cannabis.

-          Mental health and psychosocial outcomes of long-term cannabis use.

-          Long-term cannabis use and non-communicable diseases.

-          Prevention: interventions targeting families, school settings, vulnerable groups.

-          Treatment of disorders: therapies, management of acute cannabis intoxication and withdrawal, relapse prevention.

How has WHO judged the evidence?

First requirement: Evidence of an association between cannabis use and the health outcome

Second requirement: Evidence that makes reverse causation an implausible explanation of the association. To rule out that cannabis use is a consequence of the health outcome rather than the cause of it.

Third requirement: Most difficult, to assess evidence that the association is not explained by other uncontrolled or unmeasured factors (as cannabis users are likely to use other drugs, and of the difference from non-users in risk-taking etc.).

Fourth requirement: A causal relationship between cannabis use and the health outcome is biologically plausible

Other factors that may support a causal interpretation include strength of the association, dose–response relationships, specificity of the association and reversibility of the effect after removal of the drug.

How have WHO defined the harms to health?

WHO has looked at the severity of the effects do to:

-          The properties of the substance itself

-          The form and mode of administration used

-          The characteristics of the person taking the substance

-          The social context in which it is taken


What we know about the short-term effects of cannabis use

The most obvious short-term health effect of cannabis is intoxication marked by disturbances in the level of consciousness, cognition, perception, affect or behaviour, and other psychophysiological functions and responses.

A minority of first-time cannabis users become very anxious, have panic attacks, experience hallucinations and vomit. These symptoms may be sufficiently distressing to prompt affected users to seek medical care.

Acute use impairs driving and contributes to an increased risk of traffic injuries.

There is some evidence that cannabis use can trigger coronary events. Recent case reports and case series suggest that cannabis smoking may increase CVD risk in younger cannabis smokers who are otherwise at relatively low risk.

What we know about the long-term effects of regular cannabis use

Regular cannabis users can develop dependence on the drug. The risk may be around 1 in 10 among those who ever use cannabis, 1 in 6 among adolescent users, and 1 in 3 among daily users.

Withdrawal syndrome is well documented in cannabis dependence.

Growing evidence reveals that regular, heavy cannabis use during adolescence is associated with more severe and persistent negative outcomes than use during adulthood.

In a number of prospective studies there is a consistent dose−response relationship between cannabis use in adolescence and the risk of developing psychotic symptoms or schizophrenia.

The association between cannabis use and psychosis or schizophrenia has been recognized for over two decades in at least four ways:

-          Cannabis produces a full range of transient schizophrenia-like positive, negative and cognitive symptoms in some healthy individuals.

-          In those harbouring a psychotic disorder, cannabis may exacerbate symptoms, trigger relapse and have negative consequences on the course of the illness

-          With heavy cannabis use, susceptible individuals in the general population develop a psychotic illness which is associated with age of onset of use, strength of THC in the cannabis, frequency of use and duration of use.

-          Cannabis use is associated with lowering the age of onset of schizophrenia It is likely that cannabis exposure is a "component cause" that interacts with other factors to precipitate schizophrenia or a psychotic disorder, but is neither necessary nor sufficient to do so alone.
                                         

Long-term cannabis smoking produces symptoms of chronic and acute bronchitis, as well as microscopic injury to bronchial lining cells, but it does not appear to produce COPD.

Long-term heavy cannabis smoking can potentially trigger myocardial infarctions and strokes in young cannabis users.

Smoking a mix of cannabis and tobacco may increase the risk of cancer and other respiratory diseases but it has been difficult to decide whether cannabis smokers have a higher risk, over and above that of tobacco smokers.

There is suggestive evidence that testicular cancer is linked to cannabis smoking and this potential link should be investigated further.


What we know about prevention and treatment

Evidence-based preventive interventions should cover the whole prevention chain from universal and selective to indicated prevention.

Comprehensive family prevention that involves training for parents, children and the family collectively is found to be effective in reducing both lifetime cannabis use and past-year use in adolescents.

Life skills programmes that combine both a social competence curriculum and social influence approaches are shown to reduce cannabis use at 12-month follow-up and beyond.

Interactive social programmes targeting vulnerable young people is found to be effective in reducing past-month cannabis use.

A single-session brief psychological intervention of 30−45 minutes increases the chances of cannabis cessation if people are not dependent on cannabis.

Many people with cannabis-use disorders cease cannabis use without treatment.

For people who are dependent on cannabis, family interventions are effective for adolescents, and CBT, MET and PPS are effective in adults.