Resumen

Introduction: Chemsex, the intentional use of drugs to enhance sexual experiences among gay, bisexual, and other men who have sex with men (gbMSM), is linked to high-risk sexual behaviours and increased sexually transmitted infections (STIs). Data on its long-term evolution after implementing specific strategies in HIV settings are limited. We evaluated the incidence of drug use, sexual behaviour, STIs, and vulnerabilities over 3 years following a specific approach at the HIV Unit of Hospital Clinic in Barcelona, Spain. Methods: We included 209 gbMSM living with HIV who engaged in chemsex in a prospective cohort (2018–2022). Quarterly visits assessed sexual behaviours, drug use, and STIs screening. Data were collected via self-administered questionnaires, medical records, and microbiological tests. Statistical analyses included descriptive statistics and Poisson regression models. Results: Chemsex incidence decreased significantly (IRR 0.88, 95% CI 0.83–0.92, p < 0.001). People engaging in intravenous drug use (slamming) decreased in year 2 (IRR 0.71, 95% CI 0.52–0.98, p = 0.037) but rose non-significantly in year 3 (IRR 0.86, 95% CI 0.60–1.25, p = 0.434). High-risk sexual behaviours persisted, specifically unprotected anal sex (IRR 1.02, 95% CI 0.96–1.08, p = 0.481) and unprotected fisting (IRR 1.20, 95% CI 1.05–1.39, p = 0.010). Syphilis cases declined (IRR 0.40, 95% CI 0.26–0.60, p < 0.001). At baseline, 29% had HCV antibodies, with five new acute HCV cases. Concerns about chemsex decreased (IRR 0.52, 95% CI 0.43–0.63, p < 0.001), whereas the demand for sexuality-related assistance increased (IRR 1.53, 95% CI 1.20–1.94, p = 0.004). Loss to follow-up (21%) was greater among younger individuals, people engaging in intravenous drug use (slamming) (IRR 2.43 95% CI 1.33–4.42, p = 0.004), detectable HIV viral load (IRR 3.01, 95% CI 1.57–5.76, p = 0.001), and greater need for help (IRR 1.35, 95% CI 1.03–1.78, p = 0.03). Migrants and sex workers had higher rates of syphilis, lower education levels, and increased prevalence of STIs. Conclusion Chemsex incidence and syphilis rates declined, but persistent high-risk behaviours, subgroup vulnerabilities, and increasing demand for sexuality-related assistance require targeted interventions and comprehensive support.