Excretion of Delta9-tetrahydrocannabinol in sweat.

Author(s): Huestis MA, Scheidweiler KB, Saito T, Fortner N, Abraham T, Gustafson RA, Smith ML

Affiliation(s): Chemistry and Drug Metabolism, Intramural Research Program, National Institute on Drug Abuse, National Institutes of Health, 5500 Nathan Shock Drive, Baltimore, MD 21224, USA. mhuestis@intra.nida.nih.gov

Publication date & source: 2008-01-30, Forensic Sci Int., 174(2-3):173-7. Epub 2007 May 3.

Publication type: Randomized Controlled Trial; Research Support, N.I.H., Intramural; Research Support, Non-U.S. Gov't

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 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 microg/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.