How do substance and polysubstance use trajectories differ by sexual attraction from ages 17 to 24? A community-based longitudinal cohort study in Switzerland.

Introduction: Longitudinal, population-based studies of how youth substance use (SU) varies by sexual attraction, sex and their interaction remain scarce, especially in Europe. This study examines poly-SU (PSU) trajectories at 17, 20 and 24; disparities between sexual minority (SM) youth and heterosexual (HET) youth regarding these trajectories; and their correlates. Methods: We obtained data from the Zurich Project on Social Development from Childhood to Adulthood. SU was self-reported by n=1384 participants at 17, 20 and 24, and hair-tested at 20 and 24. Regression models included SM status, sex, their interaction, sociodemographic variables and psychosocial variables. This population-based longitudinal cohort analysis used linear mixed-effect models to examine developmental trajectories. Results: The proportion of SM youth increased from 11.3% at 17 to 23.4% at 24. At 20 and 24, SM were more likely than HET youth to have used cannabis, stimulants, ecstasy and hallucinogens in the past year. At 17, SM females reported high SU, which increased until 20, then plateaued or declined by 24, approaching those of HET males. SM males exhibited lower use at 17, but this sharply increased, reaching the highest levels by 24. HET females reported the lowest use. SM females had higher tobacco use, whereas SM males showed steep increases in alcohol, cannabis and stimulant use, surpassing all other groups regarding PSU by 24. Peer SU, low self-control, sensation-seeking and internalising symptoms predicted SU-related outcomes. Conclusions: Our findings on distinct developmental timing of the increases and escalation in SU highlight important opportunities for public health intervention, indicating that prevention efforts should be strategically timed and tailored to the unique escalation patterns observed among SM youth.