Background. Although cannabis is the most widely used illicit drug in the United States, few recent American studies have examined the attributes of long-term heavy cannabis users.

Method. Using a case–control design, we obtained psychological and demographic measures on 108 individuals, age 30–55, who had smoked cannabis a mean of 18000 times and a minimum of 5000 times in their lives. We compared these heavy users to 72 age-matched control subjects who had smoked at least once, but no more than 50 times in their lives.

Results. We found no significant differences between the two groups on reported levels of income and education in their families of origin. However, the heavy users themselves reported significantly lower educational attainment (P<0·001) and income (P=0·003) than the controls, even after adjustment for a large number of potentially confounding variables. When asked to rate the subjective effects of cannabis on their cognition, memory, career, social life, physical health and mental health, large majorities of heavy users (66–90%) reported a ‘negative effect’. On several measures of quality of life, heavy users also reported significantly lower levels of satisfaction than controls.

Conclusion. Both objective and self-report measures suggest numerous negative features associated with long-term heavy cannabis use. Thus, it seems important to understand why heavy users continue to smoke regularly for years, despite acknowledging these negative effects. Such an understanding may guide the development of strategies to treat cannabis dependence.