The way gay and bisexual men are using drugs to enhance sex (chemsex) is changing in Europe, especially among younger men and those new to chemsex. They are turning to a new generation of drugs, generally with shorter half-lives. These include synthetic cathinones similar to mephedrone, but there are signs that hallucinogens like LSD are also regaining popularity.

People with newer patterns of drug use and new arrivals to the chemsex scene in general may be especially at risk of HIV and sexually transmitted infections (STIs), because their adherence to PrEP seems lower than among other groups, Professor Kai Jonas of the University of Maastricht told the recent 20^th European AIDS Conference (EACS 2025) in Paris.

Jonas was presenting an analysis of the PROTECT study, a cross-sectional study, conducted in 2024, of 15,000 gay and bisexual men and trans people in 20 countries in Europe. Funded partly by ViiV Healthcare, it measured interest in using injectable PrEP, but also collected data on many different aspects of sexual and other health risks, including sexualised drug use.

“New compounds, particularly synthetic cathinones, are coming into the drug market almost daily,” Jonas said, “and what’s being cooked up in home labs is often beyond our knowledge.”

PROTECT asked participants about their demographic data, drug use, STI diagnoses in the last six months, their patterns of PrEP use and other HIV/STI prevention behaviours, their interest in injectable PrEP and their preferred sexual activities and roles in anal sex – the latter because chemsex drugs are often used for practical purposes such as relaxation and disinhibition.

The study’s 20 countries included all the western and northern European countries and most of the Mediterranean ones including Greece, Cyprus and Israel, but excluded Malta, Iceland and most of the former communist countries except Czechia. Poland was included in the PROTECT study but not in this particular analysis.

Generally, PROTECT found that poppers (nitrites) and cannabis remained among the most universally popular drugs used in sex. It found that Jonas’s own country, the Netherlands, is a particular chemsex hotspot, both due to local use but also because it is a gay tourism centre (and also a centre of the European drugs trade). GHB/GBL (gamma-hydroxybutyrate/butyrolactone) remains popular through most of western Europe. Methamphetamine (crystal meth) was not as popular as some other drugs, except in the Netherlands, UK, Czechia and Spain.

There was one very prominent ‘new kid on the block’ – 3-MMC, also called metaphedrone, an isomer (chemical mirror-image) of 4-MMC or mephedrone.

Jonas and colleagues used a technique called latent class analysis to identify different patterns of chemsex behaviour in PROTECT participants. This technique identifies groups in datasets that are not pre-assigned but instead ‘fall out’ of the data when data points (in this case, individuals) are found that cluster together in terms of similar characteristics.

They found five classes of chemsex user among the study participants.

1. ‘Traditional’ chemsex users. This group was characterised by use of cocaine, ecstasy (MDMA) and GHB/GBL, along with high rates of ketamine and methamphetamine. There were particularly high numbers of this group in the Netherlands, as well as in Czechia, Austria, Spain and Ireland. There was virtually no use of 3-MMC in this group.
2. ‘Bottom shorties’. This novel group emerged from the data due to 100% of them having used 3-MMC and also their very high usage of GHB/GBL. There was an association in this group with being the receptive partner in anal sex and Jonas said it seems that this group was using short-acting drugs in a practical way, “to facilitate muscle relaxation and disinhibition, but not to get wiped out for the whole weekend.” The effects of 3-MMC, for instance, generally last about four hours.
3. ‘Novel’ chemsex users. This was the group with the heaviest drug use, adding 3-MMC, mephedrone and other novel cathinones such as 4-MEC to the ‘traditional chemsex’ drugs. There were also signs that hallucinogens like LSD and psilocybin (magic mushrooms) were regaining popularity. This group now outnumbered the ‘traditional’ chemsex users, with high representation especially in the Netherlands, Spain, Austria and Norway, and also Germany, Switzerland, Belgium and Czechia.
4. Moderate use. This group had very low use of drugs to enhance sex apart from poppers and cannabis.
5. Younger moderate users. This group, mainly of younger men, also only had moderate use of drugs other than poppers and cannabis, but unlike the previous group also had some use of cocaine, ecstasy, 3-MMC, GHB/GBL and other drugs.

Group 3, the novel chemsex users, had the highest rates of STIs in the last six months, with 70% reporting gonorrhoea, closely followed by group 2, the ‘bottom shorties’ (63% gonorrhoea). Hepatitis C was rare overall, but was most common in group 2 (2.2%).

Group 2 had the highest uptake of HIV oral PrEP (81%), though group 3 had nearly as high usage (74%), with high rates of sub-optimal use at 33%.

The group with by far the highest rate of unmet PrEP need, however, were group 5, the ‘young moderates’. Only 30% of them had used PrEP, and those that did had the second-highest sub-optimal PrEP use at 32%. They also had the highest rate of complete discontinuation of PrEP (22%), whereas less than 10% of groups 1 and 2 discontinued PrEP, and less than 15% of the other groups. Sixty-four per cent of them were estimated to have unmet PrEP needs compared with no more than 51% in any other group.

Jonas mentioned that there were “specific unmet HIV prevention needs and interest in long-acting injectable PrEP among novel chemsex users”, although interest was high in every group, but warned of “lower HIV prevention engagement among younger moderate substance users.”

Reference

Wang HY et al (presenter Jonas K.) Chemsex, novel chemsex substances, associated risks for STIs, and an extended PrEP cascade among HIV-negative MSM, trans* individuals in 20 European countries: A latent class analysis. 20^th European AIDS Conference, Paris, abstract PS15.3, 2025.