The first death in the UK solely linked to GBL has come to light as the Government moved to outlaw the drug.
GBL (Gamma-Butyrolactone) is one of a number of "legal high" drugs now banned under the Misuse of Drugs Act 1971.
The substance is now officially a Class C drug, possession of which may incur a penalty of up to two years imprisonment.
The crackdown followed the high profile case of Brighton medical student Hester Stewart, 21, who died in April after taking GBL. The blonde cheerleader student was said to have been killed by a combination of the drug and alcohol.
However, the new case reported on Wednesday is the first fatality in the UK to involve GBL alone. Doctors writing in the Journal of the Royal Society of Medicine said the 25-year-old male Londoner was found unconscious in bed by his partner, who attempted to resuscitate him and called an ambulance.
He had taken GBL the previous evening while out clubbing, and had been "acting strangely" after returning home six hours before he was found. Attempts to revive the man on the way to hospital and on arrival proved in vain. He suffered a prolonged cardiac arrest and died. A post-mortem examination revealed evidence of GBL but no sign of any other drugs, including alcohol.
The medical team, led by Dr Paul Dargan from Guy's and St Thomas' NHS Foundation Trust in London, wrote: "We report here the first UK case of a fatality related to confirmed, isolated GBL toxicity. GBL is widely used in the UK chemical industry and it is reported that over 1,000 tonnes are imported into the UK per year for industrial purposes. It is used as an intermediate solvent in the electronics industry and in the production of domestic and industrial cleaning products and paints."
GBL, which is virtually tasteless when diluted, is quickly broken down in the body to GHB, a substance that has been a Class C controlled drug since 2003.
Tests of blood, urine and tissue samples showed that the dead man had taken a quantity of GBL consistent with previous fatalities and cases of severe GHB toxicity.
Reporting on the case before the legal ban, the doctors added: "GHB and GBL are both widely used as recreational drugs due to stimulant effects, particularly on the nightclub scene. There is some evidence of increasing recreational use of GBL in a number of countries, and there has been a year-on-year increase in the GBL:GHB ratio in patients presenting with GBL/GHB toxicity to our clinical service in London. It is likely that, at least in part, this is related to the disparity in the legal status of GBL and GHB and, therefore, the easier availability of GBL to users."