Objectives Chemsex refers to the use of sex‐enhancing drugs among men who have sex with men (MSM) in combination with specific sexual and social behaviours. Longitudinal data on this development and the associated health risks are scarce. Methods Data on all recreational drugs reported in the Swiss HIV Cohort Study (SHCS) from 2007 to 2017 were collected. Drug use was analysed longitudinally for all drug classes. In addition, potential associations between patient characteristics and the consumption of methamphetamine, γ‐hydroxybutric acid/γ‐butyrolactone (GHB/GBL), 3,4‐methylenedioxymethamphetamine (MDMA/XTC), cocaine and amphetamine were analysed. Results We analysed 166 167 follow‐up entries for 12 527 SHCS participants, including 7101 free text field entries containing information about recreational drugs other than cannabis, cocaine and heroin. Overall, we observed a stable percentage (9.0%) of recreational drug use (excluding cannabis, amyl nitrite and prescription drugs). For MSM, however, there was an increase in overall drug use from 8.8% in 2007 to 13.8% in 2017, with particularly large increases for methamphetamine (from 0.2 to 2.4%; P < 0.001) and GHB/GBL (from 1.0 to 3.4%; P < 0.001). The use of each of the potentially sex‐enhancing drugs methamphetamine, GHB/GBL, cocaine, XTC/MDMA and amphetamine was significantly associated with condomless sex with nonsteady partners, and higher prevalences of depression, syphilis and hepatitis C. Conclusions The significant increase in the use of chemsex drugs among MSM in the SHCS and the strong association with coinfections and depression highlights the need for harm reduction programmes tailored to MSM. According to our results, improving knowledge about recreational drugs is important for all health care professionals working with people living with HIV.

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Background Sexually transmited infections (STIs) are common among people with HIV (PWH), but there is limited data about risk factors and incidence of STIs in large, representative cohort studies. Methods We assessed incidence and risk factors of STIs reported by treating physicians within the Swiss HIV Cohort Study (SHCS). STIs and demographic, clinical and behavioral characteristics were prospectively collected at 6-monthly follow-up visits between October 2017 and November 2019. We used multi-level Poisson regression to assess incidence rate ratios of different STIs. Results Among 10,140 study participants, a total of 1,634 STIs in 1,029 SHCS participants were reported over 17,766 person-years of follow up (PYFUP). The overall incidence of any reported STI was 91.9 per 1,000 PYFU (95% CI 85.8 –98.5). Among the 1,634 STI episodes, there were 573 (35.1%) incident cases of syphilis, 497 gonorrhea (30.4%) and 418 chlamydia (25.6%). MSM younger than 50 years represented 21% of the study population, but accounted for 61% of reported STIs. Being male (2.03 adjusted incidence rate ratio (aIRR), 95% CI, 1.36-3.02), MSM (3.62 aIRR, 95% CI, 2.88-4.55), age group 18-34 years (1.78 aIRR, 95%CI, 1.51-2.10), ever reported sexual relationship with occasional partners (6.87 aIRR, 95%CI, 5.40-8.73) and reporting injecting drug use (2.48 aIRR, 95% CI, 1.91-3.23) were associated with a higher risk of incident STIs. Conclusion STIs were frequent among PWH and varied considerably between age and risk groups. Screening programs and recommendations for STI testing need to be adapted according to risk factors and demographic characteristics.