Co-administering cannabis with tobacco and persistent tobacco smoking after 4½ years in young adults who use stimulants: A prospective population-based study.

Tobacco smoking remains highly prevalent in high-risk groups, including young adults who use cannabis and a variety of other drugs. We examine whether co-administering cannabis with tobacco is associated with heavier and more persistent tobacco smoking compared to separate use of these substances among young adults who use drugs recreationally. Data are from a prospective population-based study of young adults residing in Queensland, Australia, who recurrently used ecstasy or methamphetamine. The mean age was 20.8 years at baseline, and 47% were female. An ordinal regression model was developed (n = 277) with levels of tobacco smoking at 4½ years as the outcome. At baseline, just under half the sample (44.6%) had not co-administered cannabis with tobacco in the last month, 9.5% rarely co-administered, 7.7% sometimes co-administered, and 38.2% always co-administered. Always co-administering cannabis with tobacco was associated with more frequent and persistent tobacco smoking at 4½ years (Odds Ratio (OR): 1.98, 95% Confidence Interval (CI): 1.02, 3.83), independently of factors including baseline frequency of cannabis and tobacco use. Young adults who use cannabis should be advised not to co-administrate cannabis with tobacco, and comprise an important target group for tobacco smoking cessation interventions.