Gamma hydroxybutyric acid (GHB) concentrations in humans and factors affecting endogenous production.

The endogenous nature of the drug of abuse gamma hydroxybutyric acid (GHB) has caused various interpretative problems for toxicologists. In order to obtain data for the presence of endogenous GHB in humans and to investigate any factors that may affect this, a volunteer study was undertaken. The GHB concentrations in 119 urine specimens from GHB-free subjects and 25 urine specimens submitted for toxicological analysis showed maximal urinary GHB concentrations of 3mg/l. Analysis of 15 plasma specimens submitted for toxicological analysis detected no measurable GHB (less than 2.5mg/l). Studies in a male and female volunteer in which different dietary food groups were ingested at weekly intervals, showed significant creatinine-independent intra-individual fluctuation with overall urine GHB concentrations between 0 and 2.55, and 0 and 2.74mg/l, respectively. Urinary concentrations did not appear to be affected by the particular dietary groups studied. The concentrations measured by gas chromatography with flame ionisation detection (GC-FID) and gas chromatography with mass spectrometry (GC-MS) lend further support to the proposed urinary and plasma interpretative cut-offs of 10 and 4mg/l, respectively, where below this it is not possible to determine whether any GHB detected is endogenous or exogenous in nature.