Passive inhalation of marihuana smoke and urinary excretion of cannabinoids

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Abstract
Three studies in which exposure to marihuana smoke was progressively increased were conducted. In each, 4 experienced marihuana users smoked marihuana cigarettes in the presence of 2 nonsmoking subjects. They were confined in a closed environment for 1 h after the smoking began. All urine voided by the nonsmoking subjects was collected separately for 24 h and analyzed for the presence of cannabinoids by the enzyme multiplied radioimmunoassay technique (EMIT) cannabinoid assay. Blood samples were drawn from one of the nonsmoking subjects in one of the studies, and .DELTA.9-tetrahydrocannabinol (THC) plasma concentrations were determined by radioimmunoassay. Of 80 urine samples collected in the 3 studies, the drug levels in only 2 slightly exceeded the value of 20 ng/ml on the calibrator of the EMIT assay. Minute but detectable concentrations were present in the plasma of the one subject from whom blood samples were obtained. In this subject, i.v. infusion of THC at the rate of 3.2 .mu.g/min for 1 h resulted in THC plasma concentrations identical to those during his passive inhalation of marihuana smoke.