Young Adult Longitudinal Patterns of Marijuana Use among US National Samples of 12th Grade Frequent Marijuana Users: A Repeated Measures Latent Class Analysis

Abstract

Background and Aims:

Long-term frequent marijuana use is associated with significant negative outcomes, yet little is known about the longitudinal course of marijuana use among those who start frequent use during adolescence. Objectives are (a) to identify latent patterns of within-person marijuana use from ages 19–30 among 12 ^th graders reporting frequent marijuana use, (b) to examine if membership in identified patterns has changed across historical time, and (c) to examine if key covariates differentiate class membership.

Design, Setting, Participants:

Longitudinal, national US panel data from 4,423 individuals (53.4% of the eligible sample; 2,744 [62%] males) who reported frequent marijuana use in 12 ^th grade (modal age 18 years; senior year cohorts 1976–2006) followed biennially from age 19/20 through 29/30.

Measurements:

Self-reported past 30-day marijuana use (frequent use defined as use on 20+ occasions), demographics, college graduation, marriage, and parenthood.

Findings:

Repeated measures latent class analysis (RMLCA) identified five latent classes of past 30-day marijuana use from ages 19/20 through 29/30: Continued Frequent Users (estimated membership 23.4%); Frequent to Non-Frequent Users (15.5%); Consistent Non-Frequent Users (18.4%); Non-Frequent Users to Discontinuers (19.5%); and Discontinuers (23.2%). In multivariable models, membership in the highest-risk latent class (Continued Frequent Users) versus one or more of the lower-risk latent classes was more likely for recent cohorts ( p=0.038 to <0.001), as well as those who did not marry ( p=0.039 to <0.001) or become parents ( p=0.001) by modal age 29/30.

Conclusions:

Nearly one in four 12 ^th grade (modal age 18 years) frequent marijuana users in the US continues to report high frequency use through age 30; the proportion continuing high frequency use across young adulthood has increased among more recent cohorts.