A longitudinal assessment of change in marijuana use with other substance use problems.

BACKGROUND: Despite increasing marijuana use rates over the past decade, the longitudinal association between marijuana use and other substance use problems among adults is unclear.

OBJECTIVES: To examine associations of self-reported changes in marijuana use and marijuana use frequency with self-reported other substance use problems over a 12-month period.

METHODS: Two waves (W1 and W2) of the Population Assessment of Tobacco and Health Study provided data. The study sample (N = 26,204, female = 13,261; male = 12,943, aged 18+) included W1-W2 never marijuana users, W1-W2 ex-users (used prior to 12 months of W1), and those who either quit, initiated, resumed, or continued marijuana use between W1 and W2. We used multinomial and binary logistic regression analyses.

RESULTS: The past-year marijuana use rate was 12.4% at W2. A quarter of W1 users quit using marijuana in the 12 months preceding their W2 interview, and one-third of all the W2 users were new/resumed users since W1. Compared to W1-W2 ex-users, W2 quitters were more likely to report alcohol use problems and tobacco addiction at W2. Compared to quitters, continued users were more likely to report alcohol use problems (RRR = 1.62, 95% CI = 1.27-2.07) and tobacco addiction (RRR = 1.37, 95% CI = 1.11-1.69). New users (RRR = 2.05, 95% CI = 1.12-3.74), resumed users (RRR = 2.69, 95% CI = 1.55-4.70), and continued users (RRR = 3.40, 95% CI = 2.08-5.55) reported more drug use problems. Compared to less frequent marijuana users, frequent users had greater odds of reporting alcohol use problems (RRR = 1.44, 95% CI = 1.21-1.72) and drug use problems (OR = 1.63, 95% CI = 1.19-2.23).

CONCLUSIONS: Given increased prevalence of marijuana use, polysubstance use problems among marijuana users should be assessed.