The authors would like to acknowledge the assistance of the following people in the preparation of this manuscript:
Dr Robert Ali, Chairman of the National Task Force on Cannabis, for his encouragement and support at all stages of the project, and the members of the Task Force for their feedback on earlier drafts of the document.
Dr Mario Argandona (WHO Programme on Substance Abuse), Dr Greg Chesher, (National Drug and Alcohol Research Centre), Paul Christie, (Project Officer, National Task Force on Cannabis), Dr Bill Corrigal (Senior Scientist, Addiction Research Foundation, Toronto), Emeritus Professor Harold Kalant (Department of Pharmacology, University of Toronto), and Dr Jean-Marie Ruel (Bureau of Dangerous Drugs, Health and Welfare Canada) for their useful comments on the whole manuscript.
The following persons are acknowledged for their expert comments on specific sections of the manuscript: Dr Peter Fried (Carleton University, Ottawa, Ontario) for his comments on reproductive effects; Dr Richard Mattick (National Drug and Alcohol Research Centre) for his comments on the dependence syndrome; Dr Peter Nelson (Southern Cross University, New South Wales) for his comments on psychological effects); Dr Mehdi Paes (Department of Psychiatry, University of Rabat, Morocco) and Professor S.M. Channabasavanna (Director, National Institute of Mental Health and NeuroSciences, Bangalore, India) for their comments on psychiatric disorders; and Professor Donald Tashkin (Division of Pulmonary and Critical Care Medicine, University of California, Los Angeles Medical School) for his comments on cardiovascular and respiratory effects.
Eva Congreve, the Archivist at the National Drug and Alcohol Research Centre, performed above and beyond the call of duty in uncomplainingly and efficiently dealing with a plethora of requests for obscure publications in esoteric journals. Without her assistance, this review would not have been half as comprehensive as we hope it has been. Peter Congreve and Keith Warren collected articles and books which made the task of reading and writing easier.
Acknowledgment is given to the Centre's secretaries, Libby Barron, Margaret Eagers and Gail Merlin, who undertook the thankless task of checking the referencing and proof reading the manuscript.
The following is a summary of the major adverse health and psychological effects of acute and chronic cannabis use, grouped according to the degree of confidence in the view that the relationship between cannabis use and the adverse effect is a causal one.
• anxiety, dysphoria, panic and paranoia, especially in naive
• cognitive impairment, especially of attention and memory, for the duration of intoxication;
• psychomotor impairment, and probably an increased risk of accident if an intoxicated person attempts to drive a motor vehicle, or operate machinery;
• an increased risk of experiencing psychotic symptoms among those who are vulnerable because of personal or family history of psychosis;
• an increased risk of low birth weight babies if cannabis is used during pregnancy.
• respiratory diseases associated with smoking as the method of
administration, such as chronic bronchitis, and the occurrence of
histopathological changes that may be precursors to the development of
• development of a cannabis dependence syndrome, characterised by an inability to abstain from or to control cannabis use;
• subtle forms of cognitive impairment, most particularly of attention and memory, which persist while the user remains chronically intoxicated, and may or may not be reversible after prolonged abstinence from cannabis.
The following are the major possible adverse effects of chronic, heavy cannabis use which remain to be confirmed by further research:
• an increased risk of developing cancers of the aerodigestive
tract, i.e. oral cavity, pharynx, and oesophagus;
• an increased risk of leukemia among offspring exposed while in utero;
• a decline in occupational performance marked by underachievement in adults in occupations requiring high level cognitive skills, and impaired educational attainment in adolescents;
• birth defects occurring among children of women who used cannabis during their pregnancies.
The health risks of alcohol, tobacco and cannabis use
Alcohol. The major risks of acute cannabis use are similar to the acute risks of alcohol intoxication in a number of respects. First, both drugs produce psychomotor and cognitive impairment. The impairment produced by alcohol increases risks of various kinds of accident. It remains to be determined whether cannabis intoxication produces similar increases in accidental injury and death, although on balance it probably does. Second, substantial doses of alcohol taken during the first trimester of pregnancy can produce a foetal alcohol syndrome. There is suggestive but far from conclusive evidence that cannabis used during pregnancy may have similar adverse effects. Third, there is a major health risk of acute alcohol use that is not shared with cannabis. In large doses alcohol can cause death by asphyxiation, alcohol poisoning, cardiomyopathy and cardiac infarct whereas there are no recorded cases of fatalities attributable to cannabis.
Tobacco. The major acute health risks that cannabis share with tobacco
are the irritant effects of smoke upon the respiratory system, and the
stimulating effects of both THC and nicotine on the cardiovascular
system, both of which can be detrimental to persons with