Cannabis is probably the best-known drug worldwide. ∆9-THC and 11-OH-∆9-THC are the essential components that are responsible for the intoxicating and psychoactive effects. A general approval for pain therapy has been discussed for years. The analytical determination of low concentrations of ∆9-THC and its metabolites is therefore increasingly important. Quantitative tests in saliva, blood or urine require extensive analytical procedures including suitable sample preparation.