Attitudes and policies regarding recreational marijuana use are becoming increasingly permissive.
To effectively address the implications of these developments, researchers and policy makers need to understand how much and how long people use marijuana during the lifespan, and the degree to which different use patterns are associated with long-term issues such as health status.
This study found that:
To this end, Yvonne Terry-McElrath of the University of Michigan and her colleagues applied the statistical technique of latent class analysis to identify distinct patterns of marijuana use from age 18 to 50 among nearly 10,000 participants in the Monitoring the Future (MTF) study. The participants had reported their past-year marijuana use when they were high school seniors in 1976–1983, at 2-year intervals through age 30, and then at 5-year intervals until they reached age 50.
The researchers emphasize that their results do not necessarily indicate that marijuana caused the users’ health problems. “Our findings do not confirm causality,” Ms. Terry-McElrath says. “We can say that, among these participants, those who reported longer use patterns also reported higher levels of negative health outcomes, even after we controlled for numerous demographic and behavioral characteristics.” She notes that other research has also linked cannabis use to poor health.
Ms. Terry-McElrath says that her study should be interpreted with caution. She explains, “The primary strength of our analyses, being able to follow samples of U.S. respondents from age 18 through 50, is also a limitation.” Findings based on data from particular high school classes may not apply to other groups of people, such as those who did not complete high school or who graduated in earlier or later years. The evolution of marijuana laws, perceptions of risk, and the potency of the drug further complicate interpretation.
Ms. Terry-McElrath suggests that marijuana users today are likely, by and large, to be experiencing use patterns similar to those that she and her colleagues identified. “As long as historical or geographic differences in the initial prevalence of marijuana use are accounted for, the patterns that we observed would likely be similar—at least in environments characterized primarily by consistent marijuana prohibition policy,” she says.
“However, because of the rapidly changing policy and broader social context related to marijuana use, it is important to continue examining long-term use patterns and possible health consequences by following current teens and young adults into middle adulthood. To the degree that marijuana use becomes normative—similar to alcohol use—we may find there is a larger class of individuals who either begin or continue to use marijuana moderately across the lifespan.”
Source: National Institute on Drug Abuse