Experts believe more needs to be done to warn people of the dangers of 'chemsex', the act of having sex for hours or even days at a time while under the influence of drugs. Researchers at the British Medical Journal (BMJ) say the rising popularity of chemsex parties, usually involving groups of gay men, could be putting those taking part at higher risk of sexually transmitted diseases, as well as serious mental health problems through drug dependence.

The experts, specialists working in sexual health and substance abuse in London, say chemsex parties usually involve the taking of drugs such as mephedrone, crystal meth and GHB, as they "facilitate sustained arousal and induce a feeling of instant rapport with sexual partners".

Research suggests the drugs also help users manage negative feelings, such as a lack of confidence, internalised homophobia and stigma about their HIV status. As a result, mental health services are seeing a "small but important" uptake in services by chemsex drug users who have gained a "dangerous physiological dependence".

Chemsex participants describe "losing days" — not sleeping or eating for up to 72 hours — after taking drugs, with data from service users suggesting an average of five sexual partners per session and that unprotected sex is the norm.

Researchers have also suggested some chemsex practices, particularly intravenous drug use, are a "perfect storm" for transmission of both HIV and the hepatitis C virus. Public Health England reported an increase in STIs and hepatitis C among men who have sex with men, as well as an increase in the injecting of amphetamines and amphetamine-like substances, such as mephedrone and crystal meth.

In an editorial, the BMJ is now suggesting addressing chemsex-related diseases and treatments "should be a public health priority".

They discussed a separate report in 2014 by Antidote, a London drugs service for lesbian, gay, bisexual and transgender people, which said 64% of attendees seeking support for drug use reported using chemsex drugs in 2013-14.

The BMI said: "Many barriers exist to chemsex drug users accessing services, including the shame and stigma often associated with drug use and ignorance of available drug services.

"However, in England funding for specialist sexual health and drugs services is waning and commissioning for these services is complex. English sexual health services tend to be open access, with costs charged back to local authorities. Drug services tend to be authority specific with users having to attend a service within their borough of residence. Despite the different funding streams, creating centres of excellence for sexual health and drug services could be a cost effective solution to diminished resources in both sectors.

Dr Richard Ma, of the Royal College of GPs' Sex Drugs and BBV Group, said: "Chemsex is a rapidly emerging pattern of drug use, not just amongst men who have sex with men as often assumed, but heterosexual patients as well.

"Taking recreational drugs during sex can lead to a number of potentially harmful side effects including facilitating the spread of common STIs and HIV, but also serious mental health problems, such as anxiety, psychoses and suicidal tendencies. As such, it is essential that both patients and healthcare professionals – including GPs and primary health care teams – are aware of these and take the issue seriously.

"The college would agree that chemsex is a public health issue and would support measures to raise awareness of its associated risks and appropriate support services in the community – as well as to help healthcare professionals to deliver the necessary care and advice to patients, without stigmatising the issue."