The anaesthetic ketamine is growing in prevalence on the UK dance scene, recent surveys have found.
Best known by the street names K, Special K and Vitamin K, ketamine is a synthetic "dissociative" anaesthetic used for medical and veterinary purposes.
Its chemical name is 2-(2-chlorophenyl)-2-(methylamino)- cyclohexanone.
First reports of ketamine's use as a recreational drug started after its release into the market in 1965.
But it wasn't until the early 1990s that the drug started becoming popular on the UK club scene as people bought it in the mistaken belief it was ecstasy.
Its popularity has waxed and waned since then but the past couple of years have seen a surge in ketamine use, according to a survey by drugs information body DrugScope, published in September.
The drug comes in various forms, most commonly as a powder, but also as a liquid and a tablet.
Ketamine is dose-specific so the amount taken determines the level of effect.
At low doses the user may feel euphoric, experience waves of energy, and possibly synaesthesia - sensations such as seeing sounds or hearing colours.
At higher doses the user might become paralysed, experience hallucinations and alternate realities, and a feeling of disassociation giving an 'out of body' experience known as the "K-hole".
The immediate physical effects are similar to exercise, an increase in heart rate, cardiac output, and blood pressure.
Although the drug has been safely used in medical and veterinary practice since the 1970s, investigations into the possibility of long term harm for recreational users have not yet been completed.
There is evidence, however, to suggest that use of the drug has an effect on memory, which persists for longer than three days after use, and becomes worse for regular users of the drug.
Recent research suggests the drug is now mainly to be found at dance/club events after a fall in the popularity of ecstasy and an increasing interest in psychedelic drugs. The cheap price of the drug is also a factor.
In the latest 2004 drugs survey from dance magazine Mixmag 43% of readers who responded had tried the drug, 17% in the last month, the highest percentage ever, and Nick Stevenson, News Editor of the magazine expects usage to rise again this year.
An earlier report suggested there were possibly 30,000 UK users taking the drug on an occasional or regular basis. Some users mix the drug with cocaine in a combination known as CK1.
From January, ketamine has been a class-C controlled drug, the same category as cannabis, anabolic steroids, and growth hormones.
The move follows a review carried out by the Advisory Council for the Misuse of Drugs Technical Committee.