Multidirectional Pathways of Tobacco and Marijuana Use, Including Comorbid Use, Among Young Adults (Aged 18-25 Years) in Texas: A Six-Wave Cross-Lagged Model.

Purpose: Prevalence of past 30-day tobacco and marijuana use are highest among young adults in the U.S., and comorbid use of these products is common. However, it is unclear whether the use of one product precedes the other-an important consideration, given the new climate surrounding marijuana legalization and the popularity of e-cigarette products.

Methods: Six-panel cross-lagged regression models, with 6 months between each panel/wave, were used to model bidirectional paths between past 30-day use and comorbid use of marijuana and tobacco products from 2014 to 2017 among young adults (N = 5,221 college students, aged 18-25 years).

Results: Combustible tobacco use and e-cigarette use were prospectively associated with greater risk of future marijuana use while controlling for the stability of use over time, age, race/ethnicity, and sex. Marijuana use was prospectively associated with greater risk of future combustible tobacco and e-cigarette use. Comorbid use was common, but while the odds of comorbid use decreased with increasing age, odds of tobacco use increased.

Conclusions: More young adults may be consolidating their use than are successfully ceasing their tobacco or marijuana use as they mature through young adulthood. Although we observed decreases in comorbid use of combustible tobacco with marijuana and e-cigarettes with marijuana, we simultaneously observed strong stability in single use of these products over time. Taken together, these results should help structure interventions specific to young adults that target use and comorbid use in early young adulthood to discourage initiation, encourage cessation, and curb subsequent escalation in later young adulthood.