Examining prevalence and correlates of cigarette and marijuana co-use among young adults using ten years of NHANES data.

Background: Prior research has documented a strong association between cigarette and marijuana use among young adults; it is critical to study patterns and risk factors for co-use.

Methods: Appended, cross-sectional National Health and Nutrition Examination Survey (NHANES) data were used to assess prevalence and correlates of cigarette and marijuana co-use among young adults (ages 21-30) over a 10-year period (2005-2014). Respondents (unweighted sample = 4,948) were classified into four categories regarding past-month behavior: neither use, cigarette-only use, marijuana-only use, and co-use of both. Regression models were computed to predict these categories using three waves of NHANES (unweighted sample = 3,073).

Results: Prevalence of past-month cigarette use decreased from 30.9% in 2005-2006 to 23.7% in 2013-2014 (p = 0.024) while past-month marijuana use (average 18.0%) and past-month co-use (average 9.8%) remained stable during this time. Co-use differed significantly by gender (p < 0.001; average 12.9% men, 6.8% women). Co-users were less likely to be married, more likely to endorse non-Hispanic black racial identity, more likely to have engaged in non-marijuana drug use in their lifetime and more likely to drink alcohol monthly than cigarette-only users. Co-users were more likely to have depressive symptoms, ever use non-marijuana drugs, live with a smoker, and initiate marijuana at a younger age than marijuana-only users.

Conclusions: Co-use of cigarettes and marijuana remained stable but high over a ten-year period; understanding the unique characteristics, living situations, experiences, and substance use behaviors of co-users can contribute to more effective, tailored prevention and education strategies to reduce the burden of comorbid cigarette and marijuana use.