A double-blind, randomized, placebo-controlled, cross-over study on the pharmacokinetics and effects of cannabis

Systematic measurements of the concentration of the psycho-active substance delta-9- tetrahydrocannabinol (THC) in 'netherweed' cannabis obtained from coffeeshops in the Netherlands have revealed that the mean THC concentrations have steadily increased from circa 8.6% in December 1999-January 2000 to 17.7% in December 2004-January 2005. Smoking cannabis with higher THC contents (external exposure: 9.75 to 23.12% THC) was associated with a dose-related increase of the serum concentrations of THC (internal exposure). Smoking cannabis with higher THC contents was also associated with a dose-related increase of physical effects (such as increase of heart rate, and decrease of blood pressure) and psychomotor effects (such as reacting more slowly, being less concentrated, making more mistakes during testing, having decreased functioning of motor control, and having more drowsiness). Results as mentioned above were derived from a clinical study with 24 cannabis users