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Forensic Aspects of Cannabinoid Pharmacokinetics and Pharmacodynamics

Zveřejnil: Mgr. Jaroslav Vacek | Poslední úprava: 25.02.2011


Balíková, M. A. & Huestis, M. A. (2008). Forensic Aspects of Cannabinoid Pharmacokinetics and Pharmacodynamics. Adiktologie, (8)3, 218-235.

Klíčová slova

cannabis – pharmacokinetics – psychotropic effects – traffic risk


Cannabis is one of the most abused drugs throughout the world due to its psychotropic effects. In many countries, consumption is increasing (UNODC, 2008). Although some cannabinoids in the plant Cannabis sativa have significant psychoactivity (delta-9-tetrahydrocannabinol, THC), some have low or no psychoactivity but important analgesic, immunosupressive, antiemetic, and/or antiinflammatory properties (cannabidiol, cannabigerol). There has been considerable effort to separate the therapeutic and euphoric effects of cannabis. Medical benefits of specific cannabinoids may suppress adverse symptoms of serious diseases and enhance quality of life. However, there is no doubt that the long-term chronic consumption of illegal cannabis impairs human health including lung
damage, behavioral changes, cardiovascular, reproductive, and immunological adverse effects and exacerbation of psychiatric problems in vulnerable persons. There is sufficient evidence from controlled experimental and epidemiological studies to indicate an increased risk of crashes among drivers under the influence of cannabis. Delta-9-tetrahydrocannabinol (THC) impairs cognition, psychomotor behavior and driving performace in a dose-related manner. Combined use of cannabis and alcohol produces more severe impairment. The lipophilic character of THC results in accumulation of the drug in fat tissues, where its slow redistribution into blood is the rate-limiting process in its terminal elimination. It is much more difficult to correlate impairment with THC blood concentration than to relate impairment to ethanol concentration. THC blood concentrations peak within minutes, before the end of smoking, with a subsequent rapid decrease to the analytical limit of detection. Peak euphoria is delayed compared to peak blood concentrations; most physiological and behavioral effects return to baseline within 3-5 hours. In forensic investigations, it is necessary to differentiate impaired drivers from those who are no longer under the influence. Kinetic models have been developed to estimate time of last cannabis smoking to enable differentiation between recent and past consumption, and frequent from occasional use. Monitoring THC whole blood and plasma concentrations in the heaviest long-term chronic cannabis users during a week of monitored abstinence revealed measurable THC for up to 7 days, although in the majority of participants THC concentrations were below a limit of quantification of 1 ng/mL within 24 h. Culpability studies have shown a significant positive correlation between THC concentrations and driving impairment. Therefore, it is difficult to establish a per se THC blood limit that will identify subjects under the influence of THC, without misidentifying residual THC excretion in the heaviest cannabis users. Low per se limits, close to the analytical limits of quantification are needed for accident prevention, but documentation of observed impaired driving may be necessary to fairly enforce safe driving regulations.

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