Link between cannabis and mortality is still not established

A recent editorial in this journal implied that as many as 30 000 deaths in Britain every year might be caused by smoking cannabis.1 The authors reasoned that since the prevalence of smoking cannabis is about one quarter that of smoking tobacco the number of deaths attributable to smoking cannabis might be about one quarter of the number attributed to tobacco cigarettes (about 120 000). The idea that the use of cannabis increases mortality is worthy of closer examination. How do we assess this issue?

Firstly, we need to examine published data regarding use of cannabis and mortality. These data come from two large studies. The first study done in a cohort of 45 450 male Swedish conscripts, age 18-20 when interviewed about the use of cannabis, reported no increase in the 15 year mortality associated with the use of cannabis after social factors were taken into account.2 The second study was performed in a cohort of 65 171 men and women age 15-49, who were members of a large health maintenance organisation in California, United States. They completed a questionnaire assessing their use of cannabis, and reported no increase in mortality associated with use …