The first known death from a drug popular with clubbers has emerged the day the government banned it.
Toxicologists in London found that a 25-year-old man died hours after taking GBL on its own while out clubbing.
Writing in the Journal of the Royal Society of Medicine, they said the man was found unconscious by his partner who had tried to resuscitate him.
The drug is among a list of so-called "legal highs" banned on Wednesday amid growing evidence of their harm.
The report in the journal details how the man had been previously fit and healthy - but had returned home from a night out in 2008 "acting strangely".
When the ambulance arrived, the crew continued attempts to resuscitate the man. There were further attempts to revive him when he reached hospital, but he died from a prolonged cardiac arrest.
Writing before the ban came into force, the team said that the man's post-mortem revealed the presence of GBL in his body - but no sign of alcohol or any other drug.
Once in the body, chemical reactions turn GBL into another drug, GHB, which has been banned since 2003.
The post-mortem found that the quantity of GBL in the man's body was consistent with the amount seen in previous fatal overdoses involving GHB.
Dr Paul Dargan, of Guy's and St Thomas' NHS Foundation Trust in London, wrote: "There are numerous reported fatalities related to GHB ingestion.
"However, although there has been media coverage of potential GBL-related fatalities in the UK, there have only been three previous reports of GBL-related fatality, two in Germany and one in the USA.
"We report here the first case of a fatality related to isolated GBL toxicity in the UK, which we feel supports the case for classifying GBL similar to that of GHB."
GBL is used in the chemical industry and appears in cleaning products, solvents and paints.
The doctors wrote that medical records showed that there had been recent increases in the number of patients suffering overdoses caused by GBL - almost certainly caused by the fact that GHB had been made a controlled drug in 2003.
The Home Office decision to ban GBL and other "legal highs" came after a recommendation from the Advisory Council on the Misuse of Drugs and a campaign by the family of 21-year-old Hester Stewart.
The Brighton medical student died in April after taking GBL and drinking alcohol. Her parents lobbied the government to ban the drug saying they could not understand why it was banned for personal use in the US and Canada, but not in the UK.
By Dominic Casciani
December 23, 2009
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GBL drug death identified by UK doctors