[Variability of cannabinoid findings in blood]

Cannabis products have been administered for many centuries; today, cannabis is the most widely used illegal drug all over the world. Nevertheless, the interpretation of cannabis findings in blood with regard to consumption behaviour and/or estimating the elapsed time since the last cannabis use is still a very challenging task. A wide variation of pharmacokinetic parameters has been observed even in experimental studies. Different chemical structures of precursors, smoking dynamics, pyrolysis of phytocannabinoids and frequency of drug use affect the amount of THC absorbed. Polymorphic enzymes are involved in phase-I-metabolism of THC. Pharmacological effects of other cannabinoids or medication on the pharmacokinetics of THC have not yet been studied in detail. Hydrolysis of cannabis conjugates may occur during storage of blood samples and processing of specimens for analysis; knowledge on the stability of cannabinoids in forensic specimens is still poor. Whether determination of cannabinoid conjugates may be useful is a matter of further consideration. At present, the broad variation of pharmacokinetic parameters and the limiting factors discussed in the present paper should be taken into account when using data from experimental studies for interpretation of analytical results in forensic case work.