This chapter compares the most probable adverse health effects of cannabis use with those of alcohol and tobacco, two commonly used psychoactive substances in Western societies that produce similar effects (alcohol) and share a common route of administration (smoking) with cannabis.

Anyone attempting to make such comparisons confronts a number of difficulties. The first are difficulties in making causal inferences about relationships between cannabis use and the adverse health outcomes (see the introduction to Section 2). The second difficulty is the dearth of information on the size of many of the risks that cannabis use poses for users. Both reflect the lack of epidemiological research on the health effects of cannabis by comparison with the research on the health risks of alcohol and tobacco use.

Our approach

We approach these issues as follows. First, we identify the most probable causal relationships between cannabis use and specific health effects using standard criteria for assessing evidence for causal relationships. Second, in so far as it is possible, we have quantified the severity of personal and public health risk for each adverse health effect that can be attributed to cannabis. We have estimated approximate relative risk, and the prevalence of the relevant pattern of use. Third, we have compared these approximate estimates with best estimates of the mortality and morbidity burden of alcohol and tobacco. This has been done initially by indicating the specific adverse health effects that cannabis may share with alcohol and nicotine. This is followed by a discussion of the probable quantitative risks of cannabis by comparison with those of alcohol and nicotine. The results of recent studies of the burden of disease are also discussed.

In making these comparisons, we acknowledge two limitations. First, we have relied on epidemiological evidence on the health consequences of cannabis use that is largely based on studies conducted in the English-speaking countries, and most particularly the United States. Second, the comparisons of health effects are also largely confined to effects on the health of users.