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Major Studies of Drugs and Drug Policy
Canadian Senate Special Committee on Illegal Drugs
Volume I - General Orientation

Chapter 7 - Cannabis: Effects and Consequences



In total, based on all the data from the research and the testimony heard regarding the effects and consequences of cannabis use, the Committee concludes that the state of knowledge supports the belief that, for the vast majority of recreational users, cannabis use presents no harmful consequences for physical, psychological or social well-being in either the short or the long term.

More specifically, this conclusion is based on the following conclusions.



Conclusions of Chapter 7

Acute effects of cannabis




Distinctions between uses









At-risk use and heavy use in adults








Any use in those under age 16 is high-risk use







Consequences of heavy use

      The immediate effects of cannabis are characterized by feelings of euphoria, relaxation and sociability; they are accompanied by impairment of short-term memory, concentration and some psychomotor skills.



      For purposes of public policy, the Committee does not feel that the traditional distinctions between acute and chronic effects are useful.

      Similarly, the Committee does not feel the dichotomy of use and dependence is useful.

      The research data does not allow for a clear distinction between use, at-risk use and heavy use.

      The amount consumed is an indicator, but other factors, psychosocial factors and factors relating to the context of use and the quality of the substance, are equally determining in the passage from use to at-risk use and heavy use.


      Nevertheless, the Committee feels that for people over the age of 16, at-risk use lies within the range of 0.1 to 1 gram per day; anything more than that is heavy use, which can have negative consequences on the physical, psychological and social well-being of the user.

      According to this distinction, and in accordance with the epidemiological data available, there is reason to believe that approximately 100,000 Canadians could be at-risk users and approximately 80,000 could be heavy users.


      The Committee feels that, because of its potential effects on the endogenous cannabinoid system and cognitive and psychosocial functions, any use in those under age 16 is at-risk use;

      Our estimation would suggest that approximately 50,000 youths fall in this category.

      For those between the ages of 16 and 18, heavy use is not necessarily daily use but use in the morning, alone or during school activities;


      Heavy use of smoked cannabis can have certain negative consequences for physical health, in particular for the respiratory system (chronic bronchitis, cancer of the upper respiratory tract).

      Heavy use of cannabis can result in negative psychological consequences for users, in particular impaired concentration and learning and, in rare cases and with people already predisposed, psychotic and schizophrenic episodes.


      Heavy use of cannabis can result in consequences for a users social well-being, in particular their occupational and social situation and their ability to perform tasks.

      Heavy use of cannabis can result in dependence requiring treatment; however, dependence caused by cannabis is less severe and less frequent that dependence on other psychotropic substances, including alcohol and tobacco.




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