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Desrosiers NA, Himes SK, Scheidweiler KB, Concheiro-Guisan M, Gorelick DA, Huestis MA. 
“Phase I and II Cannabinoid Disposition in Blood and Plasma of Occasional and Frequent Smokers Following Controlled Smoked Cannabis”. 
Clin Chem. 2014 Feb 24.
Delta-(9)-Tetrahydrocannabinol (THC), 11-hydroxy-THC (11-OH-THC), and 11-nor-9-carboxy-THC (THCCOOH) have been reported in blood from frequent cannabis smokers for an extended time during abstinence. We compared THC, 11-OH-THC, THCCOOH, cannabidiol, cannabinol, THC-glucuronide, and THCCOO-glucuronide blood and plasma disposition in frequent and occasional cannabis smokers.

METHODS: Frequent and occasional smokers resided on a closed research unit and smoked one 6.8 THC cannabis cigarette ad libitum. Blood and plasma cannabinoids were quantified on admission (approximately 19 h before), 1 h before, and up to 15 times (0.5-30 h) after smoking.

RESULTS: Cannabinoid blood and plasma concentrations were significantly higher in frequent smokers compared with occasional smokers at most time points for THC and 11-OH-THC and at all time points for THCCOOH and THCCOO-glucuronide. Cannabidiol, cannabinol, and THC-glucuronide were not significantly different at any time point. Overall blood and plasma cannabinoid concentrations were significantly higher in frequent smokers for THC, 11-OH-THC, THCCOOH, and THCCOO-glucuronide, with and without accounting for baseline concentrations. For blood THC > 5 ug/L, median (range) time of last detection was 3.5 h (1.1-gt;;30 h) in frequent smokers and 1.0 h (0-2.1 h) in 8 occasional smokers; 2 individuals had no samples with THC > 5 ug/L. CONCLUSIONS: Cannabis smoking history plays a major role in cannabinoid detection. These differences may impact clinical and impaired driving drug detection. The presence of cannabidiol, cannabinol, or THC-glucuronide indicates recent use, but their absence does not exclude it.
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