FIGURE 3.1 Age distribution of marijuana users among the general population in 1996. (Adapted from Marijuana and Medicine: Assessing the Science Base. Institute of Medicine. 1999. Washington, DC: National Academy Press.)

said they stopped when they found themselves in positions of responsibility or in less frequent contact with other marijuana users. They also cited parental disapproval more often than peer disapproval as a factor in their decision to give up marijuana.

But people who turn to marijuana to relieve medical symptoms—most of whom are older than 35—face an entirely different set of circumstances than do youthful recreational users. There are no existing scientific studies of the relationship between medical marijuana use and abuse. However, several individual and environmental factors appear to influence whether a particular person is likely to abuse or become addicted to a given drug. Each of these criteria bears consideration in calculating the risks posed by medical marijuana.

Some segments of the population appear to be more susceptible to drug dependence in general than others. For example, national survey results indicate that men are 1.6 times more likely to