Sex during the illegal drug-fuelled sessions is often unprotected - with those having chemsex reporting an average five sexual partners per session, according to the British Medical Journal.
'Mephedrone and crystal meth are physiological stimulants, increasing heart rate and blood pressure, as well as triggering euphoria and sexual arousal.
'GHB (and its precursor GBL) is a powerful psychological disinhibitor and also a mild anaesthetic.'
The experts said the increase in chemsex was also putting people at risk of serious mental health problems caused by drug dependencies.>The authors of the report said there were many barriers for people who want to get help, including the shame and stigma often associated with drug use and ignorance of available drug services.
Some services are now developing specific chemsex and 'party drug' clinics, with specialist mental health support and help for withdrawing from the drugs.
But they warned that users often describe 'losing days' - not sleeping or eating for up to 72 hours - which 'may harm their general health'.