INTRODUCTION There is a dire paucity of research into the burden, correlates and motives of substance use among trans young people in Australia.

METHOD Using data from a national survey of Australian trans young people (N = 859, M = 19.4), we estimated prevalence of past 6-month substance use (tobacco, alcohol, cannabis, other drugs) and lifetime substance use disorder diagnoses. Covariate-adjusted multivariate logistic regression models tested associations between substance use types with 18 interpersonal factors. Open-ended responses regarding substance use motives (n = 489) were qualitatively analysed using thematic analysis with an interpretative phenomenological approach.

RESULTS Prevalence of lifetime substance use disorder diagnosis was 13.5% (95% confidence interval [CI] 11.1, 16.1). Alcohol use was most reported (72.4%; 95% CI 68.9, 75.6) followed by tobacco (31.1%; 95% CI 27.7, 34.6) and cannabis (30.6%; 95% CI 27.2, 34.2). Trans women reported highest rates of alcohol and cannabis use; use of other drugs was highest among trans men. Highest risk of substance use was observed among trans youth who experienced discrimination, intimate partner abuse, peer rejection and lack of family support (adjusted odds ratios ranging 1.5 to 3.0). Four multi-levelled themes of substance use motives were identified: circumstantial use, somatic use, feeling better about oneself and one's life, and harm reduction.

DISCUSSION AND CONCLUSIONS While substance use among trans young is largely circumstantial, hedonistic and altruistic, facilitating self-exploration, friendship and community connectedness, substance use among trans young people is highly prevalent and may be used to cope with sleep difficulties, depression/anxiety and cisnormativity, including delays and waitlists for accessing gender-affirming care.