Background Chemsex involves the use of psychoactive drugs in a sexual context and is a growing phenomenon among men who have sex with men (MSM) and pre-exposure prophylaxis (PrEP) users. Investigating how its negative consequences can be avoided is important. The objective of this study was to explore the perceived impact of chemsex, the willingness to reduce chemsex activities and associated risks and preferred interventions to do so among PrEP users. Methods We analysed data from an online survey among PrEP users in Belgium. Chemsex was assessed in two questionnaires distributed between September 2020 and January 2022. Results A total of 326 participants completed the baseline questionnaire, and 186 the follow-up questionnaire. About one in three participants (36.5%, 119/326) reported engaging in chemsex, and half of those (49.6%, 59/119) were willing to reduce chemsex-related risks. The most preferred strategies for reducing risks were online support via an app (37.3%, 22/59) and face-to-face counselling with a health care professional (30.5%, 18/59). Among those reporting recent chemsex in the follow-up questionnaire, about one in five (21.9%, 14/64) wanted to reduce or stop chemsex activities. About 23.4% (15/64) also reported experiencing negative consequences of chemsex on their health, social or professional life. Conclusion Our findings show that one in four PrEP users engaging in chemsex experienced negative consequences of these activities and about one in five was willing to reduce or stop chemsex activities. We recommend embedding comprehensive chemsex support in the PrEP package of care and developing novel tools and interventions in order to reach maximum impact.