Urinary excretion profiles of 11-nor-9-carboxy-D9-tetrahydrocannabinol in humans after single smoked doses of marijuana
Interpretation of marijuana-positive urine tests requires an understanding of the excretion pattern of marijuana metabolites in humans. However, limited urinary excretion data from controlled clinical studies of marijuana use are available. In this study, six subjects smoked a single marijuana cigarette (placebo, 1.75% D9-tetrahydrocannabinol [THC], or 3.55% THC) each week while residing on the clinical ward of the Addiction Research Center. Individual urine specimens were collected for 7 days after drug administration and analyzed for 11-nor-9-carboxy-D9-tetrahydrocannabinol (THCCOOH) by gas chromatography–mass spectrometry (GC–MS) with a limit of detection of 0.5 ng/mL. Substantial intersubject variability in patterns of THCCOOH excretion was noted between subjects and between doses. Mean THCCOOH concentrations in the first urine collections were 47 ± 22.3 ng/mL and 75.3 ± 48.9 ng/mL after the 1.75 and 3.55% THC cigarettes, respectively. Mean peak urine THCCOOH concentrations averaged 89.8 ± 31.9 ng/mL and 153.4 ± 49.2 ng/mL after smoking of approximately 15.8 mg and 33.8 mg THC, respectively. The mean times of peak urine concentration were 7.7 ± 0.8 h after the 1.75% THC and 13.9 ± 3.5 h after the 3.55% THC dose. Mean GC–MS THCCOOH detection times for the last positive urine sample after the smoking of a single 1.75 or 3.55% THC cigarette were 33.7 ± 9.2 h and 88.6 ± 9.5 h, respectively, when a 15-ng/mL cutoff concentration was used. An average of 93.9 ± 24.5 µg THCCOOH (range, 34.6–171.6 µg) was excreted by each subject during the 7-day period after smoking of a single 1.75% THC cigarette. The average amount of THCCOOH excreted in the same time period after the high dose was 197.4 ± 33.6 µg (range, 107.5–305.0 µg). This represented an average of only 0.54 ± 0.14% and 0.53 ± 0.09% of the original amount of THC in the low- and high-dose cigarettes, respectively. These data provide a detailed compilation of THCCOOH concentrations in urine after administration of marijuana that may aid in the interpretation of urine cannabinoid results.