Correlates and trends in youth co-use of marijuana and tobacco in the United States, 2005-2014.

BACKGROUND: Past-month marijuana and tobacco use (co-use) are increasing among U.S. adults, but little is known about the prevalence of co-use among U.S. youth. This study uses nationally representative data to assess the prevalence, correlates, and trends in co-use of marijuana and tobacco, tobacco-only use, and marijuana-only use among U.S. youth.

METHODS: Data came from 176,245 youth ages 12-17 who responded to the National Survey on Drug Use and Health - a nationally representative, household interview survey - between 2005 and 2014. Prevalence, demographics and substance use characteristics from 2013 to 14 were assessed across three groups: past-month users of marijuana and tobacco (co-users), past-month tobacco-only users, and past-month marijuana-only users. Multinomial logistic regression was used to assess demographic correlates of each group. Linear and quadratic trends were assessed from 2005 to 2014 using logistic regression with orthogonal polynomials.

RESULTS: In 2013-14, 5.4% of youth reported past-month co-use of tobacco and marijuana, 2.2% reported marijuana-only use, and 3.9% reported tobacco-only use. Co-use was associated with higher prevalence of past year marijuana dependence (vs. marijuana-only users), and higher past-month risky alcohol and other illicit drug use (vs. both tobacco and marijuana-only use groups). Co-use did not increase significantly between 2005 and 2014; tobacco-only use declined, and marijuana-only use increased.

CONCLUSIONS: Co-use of marijuana and tobacco is more prevalent than tobacco-only or marijuana-only use in U.S. youth. Given changing tobacco and marijuana policies, ongoing surveillance and studies that seek to increase our understanding of co-use behaviors in youth are critical.