Ingum J.^*, Bjorklund R.^**, Beylich K.M.^*

^* National Institute of Forensic Toxicology Oslo, Norway
^** National Institute of Occupational Health, Oslo, Norway

The present study examined the extent of cognitive and psychomotor impairment after intake of a cannabis-cigarette containing 20 mg of tetrahydrocannabinoI (THC), which is a dose commonly used by cannabis-smokers. Methods. The study was conducted according to a double blind and placebo-controlled crossover design. Only regular tobacco smokers, 20 to 35 years, without a history of illegal drug use were included in the study. Subjects participated two times with smoking of either tobacco (placebo) or tobacco mixed with a given amount of hashish. Blood samples were collected before and several times after smoking, and THC-concentrations were determined by GC/MS. The volunteers accomplished psychomotor and cognitive tasks as well as subjective ratings of alertness and tension before and several times after intake. Furthermore, electrocardiographic recording was conducted continuously during the first hour after intake. Results. The blood concentration of THC peaked (approximately 300-500 nM) immediately after smoking and decreased to approximately 2 nM during the first 4 hours. The heart rate increased to a maximum of about 70 % above baseline approximately 5 min after smoking, and returned to normal within 1 hour. The volunteers reported maximal effects with respect to some of the subjective scales at the end of the smoking session, whereas other subjective effects peaked about 15 min after smoking. Conclusion. Intake of 20 mg THC produces profound psychophysiological effects. The time course of these effects was similar to the time course of the blood concentrations of THC.