Gamma-butyrolactone (GBL) and 1,4-butanediol (1,4-BD) are precursor chemicals that are rapidly converted (half-life approximately 1min) to the intoxicant gamma-hydroxybutyrate (GHB) when ingested into the human body.

GHB occurs naturally in small amounts in the brain, and is recognised by specific receptors. It may be an inhibitory neuromodulator, involved among other things in the control of glucose metabolism, oxygen consumption and temperature regulation.