BACKGROUND AND AIMS: Sexual minority youth report significantly higher rates of substance use than heterosexual youth, yet a comprehensive and systematic evaluation and synthesis of the magnitude of this inequity has not been conducted. The purpose of this study was to conduct a meta-analysis to assess the magnitude of overall inequities in substance use between sexual minority and heterosexual youth and examine demographic and methodological moderating factors that might impact variability in substance use patterns.

METHODS: A meta-analysis of studies that examined sexual orientation inequities in substance use. We conducted a comprehensive literature search across four electronic databases (PubMed, APA PsycINFO, Web of Science, ProQuest; January 2008-July 2024). Studies were eligible if they included a youth participant population (mean sample age of 25 years or younger), examined differences in substance use between sexual minority and heterosexual groups, and published between 2008 and 2024 in English. Primary outcomes were any measures of substance use; secondary outcome was age of substance use initiation. Following PRISMA guidelines, reviewers independently reviewed and extracted data. Analyses employed random-effects models, with robust variance estimation to account for dependency among multiple effect sizes within studies. Analyses examined continuous and dichotomous outcomes separately. Bivariate meta-regression examined moderators.

RESULTS: Among 304 studies of 5 928 282 youth, sexual minority youth reported greater quantity and frequency of all assessed substances (i.e. alcohol, nicotine, cannabis, prescription drugs, powder cocaine, crack cocaine, meth/amphetamine, 3,4-methylenedioxymethamphetamine, heroin, and other substances) and engaged in more polysubstance use than heterosexual youth. For continuous outcomes, Hedges' g ranged from 0.10 (95% confidence interval [CI], 0.05-0.15, I = 99.52, participants = 354 201, studies = 48) for alcohol to 0.40 (95% CI, 0.21-0.59, I = 100.00, participants = 30 679, studies = 5) for mixed/polysubstance use. Dichotomous outcomes showed consistently elevated odds ratios, ranging from 1.34 (95% CI: 1.24-1.46, I = 96.01, participants = 3 500 203, studies = 128) for alcohol to 4.63 (95% CI, 2.91-7.38, I = 86.35, participants = 391 827, studies = 10) for heroin use. Sexual minority youth also had earlier ages of initiation (all substance outcomes: odds ratio, 1.45; 95% CI, 1.04-2.03, I = 95.39, participants = 619 187, studies = 11). Moderation results indicated that inequities were larger for plurisexual youth (e.g. bisexual, pansexual), sexual minority girls and young women, and adolescents 18 years of age or younger. The magnitude of inequities was also larger for lifetime measures of use compared with measures of recent use.

CONCLUSIONS: Sexual minority youth - particularly those who are plurisexual, sexual minority girls and young women, and adolescents 18 years of age or younger - appear to engage in substance use at higher rates than heterosexual youth.