Excretion of Δ9-tetrahydrocannabinol in sweat

Sweat testing is a noninvasive technique for monitoring drug exposure over a 7-day period in treatment, criminal justice, and employment settings. We evaluated Delta(9)-tetrahydrocannabinol (THC) excretion in 11 daily cannabis users after cessation of drug use. PharmChek(R) sweat patches worn for 7 days were analyzed for THC by gas chromatography-mass spectrometry (GC/MS). The limit of quantification (LOQ) for the method was 0.4 ng THC/patch. Sweat patches worn the first week of continuously monitored abstinence had THC above the United States Substance Abuse Mental Health Services Administration's proposed cutoff concentration for federal workplace testing of 1 ng THC/patch. Mean +/- S.E.M. THC concentrations were 3.85 +/- 0.86 ng THC/patch. Eight of 11 subjects had negative patches the second week and one produced THC positive patches for 4 weeks of monitored abstinence. We also tested daily and weekly sweat patches from seven subjects who were administered oral doses of up to 14.8 mg THC/day for five consecutive days. In this oral THC administration study, no daily or weekly patches had THC above the LOQ; concurrent plasma THC concentrations were all less than 6.1 mu g/L. In conclusion, using proposed federal cutoff concentrations, most daily cannabis users will have a positive sweat patch in the first week after ceasing drug use and a negative patch after subsequent weeks, although patches may remain positive for 4 weeks or more. Oral ingestion of up to 14.8 mg THC daily does not produce a THC positive sweat patch test. Published by Elsevier Ireland Ltd.