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.