LAUSR

AIMS To estimate longitudinal associations between self-reported sexual orientation and past-year polysubstance use among youth, and test how gender, age and early onset of tobacco and alcohol use contributed to variation in polysubstance use. DESIGN Longitudinal community-based cohort of US adolescents from the Growing Up Today Study (GUTS 1) (n = 16 873) followed from ages 12-29 years. SETTING United States of America. PARTICIPANTS A total of 13 519 individuals (7839 females; 5680 males) who responded to at least one of five self-administered questionnaires from 1999 to 2010. Ninety-three per cent reported their race/ethnicity as non-Hispanic white. MEASUREMENTS Multivariable repeated measures generalized estimating equations estimated relative risks (RRs) of concurrent polysubstance use (i.e. past 12-month use of three or more substances) comparing sexual orientation minority youth [i.e. mostly heterosexual (MH), bisexual (BI), gay/lesbian (GL)] to their same-gender, completely heterosexual (CH) counterparts. Mediation analyses tested whether early onset of tobacco and/or alcohol use explained relationships between sexual orientation and concurrent polysubstance use. FINDINGS Compared with their same-gender CH peers, sexual minorities evidenced higher risk for concurrent polysubstance use over all repeated measures [risk ratios (RRs) for sexual minority subgroups: from 1.63-2.91, P-values: <0.001] and for all age groups (RRs: from 1.50-4.04, P-values: < 0.05-< 0.001), except GL males aged 18-20 years. Differences between sexual minorities and CHs were larger among females than males (P-values for sexual orientation × gender interactions were < 0.05 for MHs and BIs), and among younger versus older ages (P-values for sexual orientation × age interactions were < 0.05, except for BI males). Sexual minorities' younger age of smoking and/or drinking initiation contributed to their elevated polysubstance use (% of effect explained was between 9.4-24.3, P-values: 0.04-< 0.001), except among GL males. CONCLUSIONS Sexual minority youth in the United States, and in particular younger females, appear to be at disproportionate risk for concurrent past-year polysubstance use. Early onset of smoking and drinking may contribute to elevated risk of polysubstance use among sexual minorities.