Age-Varying Trends in Co-Use of Marijuana and Heavy Episodic Drinking: Implications for Nonmedical Prescription Drug Use

Introduction: Heavy episodic drinking (HED; 4+/5+ drinks for women/men) and drinking-related harms remain critical public health concerns. Rates of daily marijuana use in 2017 were at an all-time high and perceived risk of marijuana use was at an all-time low. Many individuals use both alcohol and marijuana (“co-use”), with some using so that their effects overlap. Individuals who co-use alcohol and marijuana are consistently at heightened risk for negative outcomes including increased odds of violence, driving under the influence, becoming more intoxicated than planned, or mental health concerns. Alcohol use and marijuana use are both separately associated with subsequent risk for abuse of nonmedical prescription drugs (NMPD), but far less is known about potential implications of co-use for NMPD use. The current study aimed to (1) identify whether co-users were at greater risk for NMPD use across adulthood and to determine ages at which this association was strongest and (2) determine whether associations remain after controlling for pain symptom severity.

Methods: Data were from PATH. Participants were between ages 12-90. Analyses were restricted to past-year alcohol and/or marijuana users (n = 9865). Pain measures were only provided to those aged 18+. Most participants were men (60%) and White (66%). Approximately 55% reported marijuana use but no past-year HED (“marijuana-only users”), 30% reported past-year HED but no marijuana use (“HED-only users”), and 15% reported past-year HED and marijuana use (“co-users”). Prevalence of all three groups was highest in ages 18-25.

Results: Weighted time-varying effect models (TVEMs) indicated that the association between co-use and past-year NMPD use was significant and positive across most of adulthood. Relative to single-substance users, co-users were at significantly greater odds of past-year NMPD use from ages 18-52. Associations were strongest at ages 32-34 in which co-users were >2.5 greater odds of NMPD use than single-substance users. After controlling for pain, associations weakened but remained constant across ages 18-52 (peak OR of 2.2 around ages 36-38).

Conclusions: Co-users were at greater risk for NMPD use across most ages in adulthood. Although HED, marijuana use, and NMPD use rates were highest in young adulthood, associations were strongest in the mid-30s. Further, co-users were at more than twice the odds of NMPD use even after controlling for pain. Co-users are at substantial risk for a variety of outcomes, and may be an important subgroup to target for NMPD use. Identifying factors underlying study associations, beyond pain (e.g., contextual differences, motives for use), and how these factors may evolve with age may be important avenues for prevention and intervention work.