Proof of active cannabis use comparing 11‐hydroxy‐∆9‐tetrahydrocannabinol with 11‐nor‐9‐carboxy‐tetrahydrocannabinol concentrations

Testing hair for cannabis use has increasingly been scrutinised due to exposure to second-hand smoke or environmental contamination. Confirmation of drug use involving detection of metabolites such as 11-nor-9-carboxy-delta-9-tetrahydrocannabinol (THC-COOH) and 11-hydroxy-delta-9-tetrahydrocannabinol (THC-OH) having very rarely been considered. We developed a new, simplified procedure with regard to expenditure of time and material to determine delta-9-tetrahydrocannabinol (THC, qualitatively), as well as THC-OH and THC-COOH (quantitatively) from 587 hair samples by liquid chromatography-tandem mass spectrometry (LC-MS/MS) which was compared to hitherto established methods (n = 3). Compared to conventional methanolic extraction alkaline dissolution resulted in higher concentrations for THC-OH. Concentrations determined from specimens ranged from 0.01 to 18.7 ng THC/mg hair, 0.05-37.6 pg THC-OH/mg hair, and from 0.1 to 54.3 pg THC-COOH/mg hair. THC was detectable in 70.4% samples along with both metabolites from more than half of these samples. In 12.9% of THC-positive cases, neither THC-OH nor THC-COOH were present. In 8.9% of THC-negative cases, it was possible to detect metabolites either alone or in combination. THC-OH could more frequently be detected than THC-COOH and appeared to be less susceptible to cosmetic treatment. In summary, THC-OH turned out to be a further suitable marker to prove cannabis use. Determination of both metabolites is recommended to unequivocally differentiate consumption from external exposure or contamination.