URINARY-EXCRETION HALF-LIFE OF 11-NOR-9-CARBOXY-DELTA-9-TETRAHYDROCANNABINOL IN HUMANS

The excretion of marijuana metabolites occurs over an extended period of time. yet few studies have been designed for accurate estimation of excretion half-lives. The authors monitored excretion of the primary urinary metabolite of marijuana, 11-nor-9-carboxy-Delta 9-tetrahydroca nnabinol (THCCOOH), by gas chromatography-mass spectrometry in a contr olled clinical study of marijuana smoking that included measurement of the drug in each urine void collected during the 3-week study. Termin al excretion half-lives of THCCOOH were determined in six healthy male subjects with histories of marijuana smoking; the study was conducted on the clinical research unit of a major medical institution. Subject s smoked a single marijuana cigarette (placebo, 1.75% or 3.55% THC) ea ch week. Urine specimens (N = 953) were analyzed under blind condition s for THCCOOH by gas chromatography-mass spectrometry. Mean +/- SEM ha lf-lives calculated by the amount remaining to be excreted method afte r the low and high doses were 31.5 +/- 1.0 hours (range, 28.4 to 35.3 hours) and 28.6 +/- 1.5 hours (range, 24.9 to 34.5 hours), respectivel y, when a 7-day monitoring period was used. The amounts of THCCOOH exc reted over a 7-day period were 93.9 +/- 24.5 mu g (range, 34.6 to 171. 6 mu g) and 197.4 +/- 33.6 mu g after the low- and high-dose sessions. Longer half-lives, 44.3 to 59.9 hours, were obtained with a 14-day sa mple collection. This study documents the prolonged excretion of THCCO OH in urine and emphasizes the importance of study design in the preci se estimation of terminal excretion half-lives. A sensitive analytical method and a prolonged specimen collection period are important study considerations in the monitoring of marijuana excretion.