UCSF

Abstract Background There is elevated prevalence of marijuana use among young adults who use tobacco, but little is known about the extent of co-use generated from surveys conducted online. The purpose of the present study was to examine past-month marijuana use and the co-use of marijuana and tobacco in a convenience sample of young adult smokers with national US coverage. Methods Young adults age 18 to 25 who had smoked at least one cigarette in the past 30 days were recruited online between 4/1/09 and 12/31/10 to participate in an online survey on tobacco use. We examined past 30 day marijuana use, frequency of marijuana use, and proportion of days co-using tobacco and marijuana by demographic characteristics and daily smoking status. Results Of 3512 eligible and valid survey responses, 1808 (51.5%) smokers completed the survey. More than half (53%, n = 960) of the sample reported past-month marijuana use and reported a median use of 18 out of the past 30 days (interquartile range [IR] = 4, 30). Co-use of tobacco and marijuana occurred on nearly half (median = 45.5%; IR = 13.1, 90.3) of the days on which either substance was used and was more frequent among Caucasians, respondents living in the Northeast or in rural areas, in nonstudents versus students, and in daily versus nondaily smokers. Residence in a state with legalized medical marijuana was unrelated to co-use or even the prevalence of marijuana use in this sample. Age and household income also were unrelated to co-use of tobacco and marijuana. Conclusion These results indicate a higher prevalence of marijuana use and co-use of tobacco in young adult smokers than is reported in nationally representative surveys. Cessation treatments for young adult smokers should consider broadening intervention targets to include marijuana.