Influence of Ethanol on the Pharmacokinetic Properties of (9)-Tetrahydrocannabinol in Oral Fluid

Oral fluid (OF) tests aid in identifying drivers under the influence of drugs. In this study, 17 heavy cannabis users consumed alcohol to achieve steady blood alcohol concentrations of 0 to 0.7 g/L and smoked cannabis 3 h afterward. OF samples were obtained before and up to 4 h after smoking and on-site tests were performed (Drager DrugTest 5000 and Securetec DrugWipe 51). Maximum concentrations of tetrahydrocannabinol (THC) immedi- ately after smoking (up to 44,412 ng/g) were below 4,300 (median 377) ng/g 1 h after smoking and less than 312 (median 88) ng/g 3 h later with 5 of 49 samples negative, suggesting that recent can- nabis use might occasionally not be detectable. An influence of alcohol was not observed. Drinking 300 mL variably influenced THC concentrations (median only -29.6%), which suggests that drinking does not markedly affect on-site test performance. Many (92%) Drager tests performed 4 h after smoking were still positive, indi- cating sufficient sensitivity for recent cannabis use. Differences in the results of a roadside study with DrugTest 5000 (sensitivity 84.8%, specificity 96.0%, accuracy 84.3%) could be explained by a higher number of true negatives, differences between OF and serum and differences between occasional and chronic users.