Gamma-butyrolactone (GBL) is a potent solvent which is indispensable for industrial cleaning purposes. Unlike the metabolite gamma-hydroxybutyric acid (GHB) it is not subject to restrictions under the German Narcotics Act (BtMG) and therefore easily available in internet retailing. Studies proved a physical and mental dependence potential and complex, sometimes fatal developments in the treatment of GBL/GHB withdrawal syndromes. Because of the short half-life period it is often not possible to detect ingested GBL/GHB in blood and urine samples. In the present case interdisciplinary collaboration of psychiatry, toxicology and forensic medicine revealed a detailed consumption profile which could be verified by hair analysis. The application of hair analysis in GBL/GHB-associated cases offers information and starting points in routine forensic medicine work.