When used as a recreational drug, GHB may be found as the sodium or potassium salt, which is a white crystalline powder, or as GHB salt dissolved in water to form a clear solution – generally at a concentration of 1 gram / 1 mL and so is twice the strength of the Xyrem solution sold legally for medical use. The sodium salt of GHB has a thin, very salty, chemical taste.

GHB salt dissolved in water is potentially dangerous, as the concentration of GHB may not be known, and so the actual dose of GHB being consumed can be difficult to judge accurately. Since GHB sold for recreational use is subject to no standardisation it can be impossible to verify the actual concentration of GHB solution bought on the illicit market. Other salt forms such as calcium GHB and magnesium GHB have also been reported, but the sodium salt is by far the most common.

Some chemicals convert to GHB in the stomach and blood. GBL, or gamma-butyrolactone, is one such prodrug. Other prodrugs include 1,4-butanediol. There may be additional toxicity concerns with these precursors. 1,4-B and GBL are normally found as pure liquids, although they may be mixed with other more harmful solvents when intended for industrial use, e.g., as paint stripper or varnish thinner.

http://en.wikipedia.org/wiki/Gamma-Hydroxybutyric_acid