RELATING BLOOD-CONCENTRATIONS OF TETRAHYDROCANNABINOL AND METABOLITESTO PHARMACOLOGICAL EFFECTS AND TIME OF MARIJUANA USAGE

Pharmacokinetic and pharmacodynamic analyses of marijuana data have pr ovided new insights into the relationship of blood concentrations of t etrahydrocannabinol (THC) and metabolites to drug-induced effects. THC is rapidly absorbed and distributed to tissues; initial changes in bl ood concentrations are out of phase (hysteresis) with physiological an d behavioral changes. Once blood/tissue equilibrium is established, a direct correlation of THC blood concentration and effect is observed. Various pharmacodynamic models provide concentration estimates in the range of 7-29 ng/ml for amount of THC in blood necessary for productio n of 50% of maximal subjective high effect. Also, models have been pro posed for predicting the time of marijuana exposure from plasma concen trations of THC and THC-carboxy acid metabolite (THCCOOH). These model s were based on data from a controlled clinical study of marijuana smo king. Such models allow prediction of the elapsed time since marijuana use based on analysis for cannabinoids from a single plasma sample an d provide accompanying 95% confidence intervals around the prediction. These models may be beneficial to forensic scientists in their interp retation of cannabinoid blood data associated with accidents, criminal investigations, and traffic violations.