The sexual health expert credited with coining the term "chemsex" says drug-laced sexual encounters are increasing HIV infections in gay communities.
David Stuart, who manages the chemsex support programme at a clinic in Soho, London, was himself involved in drugs and "escorting", and contracted HIV before turning his life around after a 2005 arrest.
"These drugs are contributing phenomenally to the HIV epidemic," Stuart said in an interview at the clinic in the heart of London's gay community. "They are not the drugs of the past - happy, dancey drugs - they are much more problematic."
Stuart defines chemsex as the "use of drugs for sex" and says it is "associated with hooking up online, a high number of partners and high prevalence of HIV and sexually transmitted disease".
Chemsex drugs, such as crystal methamphetamine, mephedrone and GBL, "tapped into something that disinhibits sexual feelings," he said.
Condomless sex and communal drug use at chemsex parties are partly to blame for continued high levels of HIV infection, which have been at around 6000 people a year in the UK since 2009.
"We have about 30 people coming to our building every day, perhaps because they have been exposed to HIV, maybe through condomless sex or sharing needles. We know between 60% and 80% of those guys are here because they have been in some kind of chemsex environment," Stuart said.
The practice mushroomed with the smartphone revolution, which has facilitated the buying of drugs and the hooking up of partners through apps such as Grindr.
But Stuart believes focusing on the public health issues is to diminish the full effect that the trend is having on the community.
"GBL is a very dangerous drug. One millilitre might be enough to give me the high I am looking for, but 1.8ml could kill me. One gay man dies every 12 days from GBL in London."