PARIS — The landscape of “chemsex” in Europe is changing and could be putting users at a higher risk for sexually transmitted infections (STIs), according to new findings presented at the European AIDS Clinical Society (EACS) 2025 Annual Meeting.
Novel chemsex drugs containing synthetic cathinones or hallucinogens correlated with higher self-reported STIs and weaker oral preexposure prophylaxis (PrEP) adherence and continuation in HIV-negative men who have sex with men (MSM) and trans individuals. Crucially, in this same group, intention to use long-acting injectable PrEP (LAI-PrEP) was strikingly strong.
“We need to look out for synthetic cathinones use and how it links to behaviors, as well as how it increases STI and HIV risk if biomedical prevention isn’t used adequately, which can be the case,” Kai Jonas, PhD, professor of applied social psychology at Maastricht University, Maastricht, Netherlands, told Medscape Medical News during an on-site interview.
In addition to his concerns about synthetic cathinones, especially 3-methylmethcathinone (3-MMC), he also flagged gamma-hydroxybutyrate (GHB)/gamma-butyrolactone (GBL). “We’re really concerned about the very high risk of overdosing and the co-administration of alcohol, which can be potentially lethal.”
This means that as services strain and drugs evolve, he said, there is a need for sharper screening questions, targeted counseling, and practical offers of long-acting prevention for those most likely to benefit.
Data From 20 Countries
Jonas explained that it has been known that individuals engaging in chemsex have an increased risk for HIV and other STIs. The PROTECT Survey aimed to investigate how the landscape of sexualized substance use is changing.
The cross-sectional study explored the profiles of chemsex participants, including STI histories, HIV/STI prevention behaviors, and (un)met prevention needs. It was conducted between October 2023 and April 2024 and captured data from 14,652 HIV-negative MSM and 432 trans participants in 20 European countries.
An analysis sorted participants into distinct user profiles based on self-reported substance use, socioeconomics (age, education, employment, perceived financial status, and migration background), and preferred sexual position (insertive, versatile, receptive, or no anal sex). Information on participants’ use of PrEP was also gathered.
‘Novel Chemsex’ and ‘Bottom-Shorties’ Most Concerning
The study found that the picture of sexualized substance use across Europe is complex, with cultural and market forces shaping what people use — for example, access pathways to drugs and where drug labs are based.
“Where MDMA [3,4-methylenedioxymethamphetamine or ecstasy] is abundant, for example, you may not be very interested in crystal meth,” Jonas explained, recalling earlier Dutch patterns.
Regarding substances used for chemsex, the PROTECT dataset showed that 13.8% reported having “traditional” chemsex with, for example, methamphetamine, ketamine, GHB/GBL, mephedrone, and cocaine, while 27.7% reported having “novel” chemsex, using synthetic cathinones or hallucinogens. Of note, 3-MMC was reported by 8.7% overall, with notable country-level variation.
Five subgroups emerged: traditional chemsex users, “bottom-shorties,” novel chemsex users, moderate users, and younger moderate users.
Bottom-shorties use short-duration substances, such as GHB/GBL, poppers, and 3-MMC, to relax the body and increase sexual arousal.
The subgroups were overlaid with self-reported infections in the previous 6 months.
The bottom-shorties and novel chemsex users had higher self-reported prevalence of syphilis, gonorrhea, and hepatitis C.
The novel chemsex subgroup reported syphilis at 37.7%, gonorrhea at 70.0%, and chlamydia at 58.1%. “That pattern mirrors what frontline services in big cities have been reporting. It’s a major issue,” Jonas said, “especially when alcohol co-use with GHB/GBL raises the risk of overdose.”
If infections are the outcome, the PrEP cascade sheds light on the mechanism.
Among novel users, oral PrEP uptake was high at 73.9%, but they also had the highest suboptimal adherence (33.2%).
In contrast, younger moderate-use participants showed the lowest oral PrEP uptake (30.1%) with high suboptimal adherence (32.2%) and discontinuation (27.4%).
But a different picture emerged when the team asked about LAI-PrEP.
“They would like to have long-acting injectables because it does away with adherence issues, and it most likely keeps them on HIV prevention,” Jonas said.
Intention to use LAI-PrEP was highest in the novel chemsex group at 87.6% and lowest in the moderate users at 64%.
At the Clinic
What drives the combination of higher STI prevalence and weaker oral PrEP adherence among people using novel substances?
“Although I’m a psychologist, I can’t look into people’s minds. We don’t have a good explanation,” Jonas said. But he points to the inherent complexity of polysubstance use. “You’re combining uppers and downers” and the very practical difficulties that follow, he said. “Most likely [they] have difficulties planning, making, and following up with sexual health appointments.”
Stigma and reluctance to engage with counselling add another barrier at a time when specialized services are faced with budget cuts, creating a disconnect between people’s needs and what healthcare can offer.
For clinicians, the takeaway is to pivot screening and prevention to what people are actually using.
Jonas advised healthcare professionals not only to ask just whether they are doing chemsex but also to ask what they are using. The use of synthetic cathinones should raise alarm bells that a higher risk is involved, he said.
He also emphasized behavior-anchored risk profiles, such as bottom-shorties, because they reflect how and when people seek to enhance or facilitate sex.
“If you take crystal meth on a Friday evening, you can write off most of your weekend. But if you take GHB and 3-MMC on a Friday evening…you’re good by Saturday…and you can do other things,” he explained.
Despite the risks, traditional chemsex users “seem to know their game more,” Jonas observed. “Their levels of PrEP uptake and their fairly good adherence and lower discontinuation rates suggest they are also more in control of their sexual health.”
The contrast with novel substance users, who have poorer adherence, suggests a clear, near-term need to expand access to LAI-PrEP where the risk is highest.
‘Surprising’ Results
The findings regarding inferior PrEP adherence among users of specific newly engineered drugs are “very worrisome,” said Udi Davidovich, PhD, clinical psychologist and senior researcher at the Department of Research, Public Health Service of Amsterdam, in collaboration with the Department of Social Psychology, University of Amsterdam, Amsterdam, Netherlands, commenting for Medscape Medical News. He was not involved in the study.
The results are surprising, he said, because previous studies have shown that PrEP adherence was unaffected in chemsex users, but this could be because those studied belonged to the traditional group.
“Zimmermann et al demonstrated in a series of qualitative studies that PrEP was actually used as a means to experiment more freely with drug use while maintaining peace of mind regarding the risk of HIV acquisition,” he explained.
“If new types of chems do in fact interfere with PrEP adherence, this represents genuinely novel and concerning news for HIV prevention,” he remarked.
“These findings call for a deeper understanding of the mechanisms by which these new substances affect PrEP use and also their potential influence on ART adherence among people living with HIV. For both groups, an immediate solution could lie in long-acting injectable formulations that can compensate for suboptimal adherence. However, adherence to injection regimens within these groups will also require careful evaluation.”
The PROTECT Survey was co-funded by ViiV Healthcare, but the analysis was conducted independently from ViiV. Jonas and Davidovich reported receiving unconditional research grants from ViiV and Gilead, in addition to speaker and advisory board participation with ViiV.
By Becky McCall, MSc, MScPh
Source : Medscape
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