U.S. Patterns of Marijuana Use from Age 18 to 50
A typical path of marijuana use across the life course involves increased use during the late teens, peak use during the early 20s, and decrease thereafter. Looking at data of marijuana use across adulthood, can we see a variety of patterns as people age? Do some of the patterns cause more harm in the long run?
A recent study by YSI researchers examined past 12-month marijuana use from age 18 to 50 in the U.S. The study explored types of use that are not necessarily evident in the data but can be found via latent class analysis (LCA). LCA was redone at points over time for individuals from age 18 to 50 (RMLCA, or repeated measures latent class analysis). Almost 10,000 participants in the study were first surveyed as 12th graders in the Monitoring the Future project from 1976 to 1983. They were then surveyed every other year to age 29 and every 5 years to age 50.
The study found seven latent classes of past 12-month marijuana use and then described associations between latent classes and health outcomes at age 50. The latent classes included one class of non-users (44%), two classes with shorter-term use (28%), and four classes with longer-term use that was moderate or heavy (28%). About one half of the respondents were members of latent classes with declining use across age: Some moved from moderate use to no use by the early to mid-20s; and some moved from heavy to moderate use followed by moving to no use by age 30 or 40. Reducing use was likely during the early and late 20s. Interestingly, there was no latent class for increasing to a higher use level after age 18. This does not mean that no individuals moved to heavier marijuana use after adolescence; there were simply not enough people with such a path to form a unique class. This points to the importance of preventing heavy marijuana use during adolescence, because taking up heavy marijuana use thereafter is not that common.
Certain latent classes of marijuana use were associated with certain demographics. Members of classes with higher marijuana use intensity and/or duration were more likely to be male, to binge drink and smoke cigarettes at 18, to have parents with more education, to have income from welfare or unemployment at 35 to 45, and to increase alcohol and cigarette use from 35 to 45.
Persistent marijuana use into middle adulthood is linked to higher odds of negative health outcomes. As marijuana use increased across latent classes, there were higher odds of reporting alcohol and drug problems. Persistent moderate and heavy marijuana use was associated with higher odds of cognitive problems at age 50. Longer-term moderate or heavy use was also linked with higher odds of doctor visits for physical illness at age 50.
Terry-McElrath, Y. M., O’Malley, P. M., Johnston, L. D., Bray, B. C., Patrick, M. E., & Schulenberg, J. E. (2017). Longitudinal patterns of marijuana use across ages 18-50 in a U.S. national sample: A descriptive examination of predictors and health correlates of repeated measures latent class membership. Drug and Alcohol Dependence, 171, 70-83.