The effect of (-) trans-delta9-tetrahydrocannabinol, alone and in combination with ethanol, on human performance.

Twenty five volunteers received (-) trans-delta9-tetrahydrocannabinol (THC) (320 microgram/kg) or placebo (both orally, T0), and, 60 min later, they consumed an ethanolic beverage (0.54 g/kg) or placebo. The effects of this medication were measured at T1 (100 min after THC ingestion), T2 (160 min), T3 (220 min) and T4 (280 min) using a battery of cognitive, perceptual and motor function tests. Factorial analysis indicated that the test procedures could be adequately expressed by four rotated factors: a reaction speed factor (I'), a cognitive factor (II'), a standing steadiness factor (III') and a psychomotor coordination factor (IV'). The first principal component (I) was used as a measure of general performance across the whole test battery. Both THC and ethanol produced significant decrements in the general performance factor. Ethanol produced significant decrements in standing steadiness and psychomotor coordination, while THC caused a significant deterioration in performance on all the four rotated factors. In all cases the peak effect of ethanol occurred at T1 and by T4 the effect had worn off. The performance decrements induced by THC were slower in onset and lasted longer than those induced by ethanol. In general, the peak effect of THC occurred at T1 and T2. There was no evidence of any interaction between THC and ethanol, and the effects of a combination of THC and ethanol were no more than additive. THC (but not ethanol) produced a significant rise in pulse rate. Prior administration of THC did not significantly affect the blood ethanol levels obtained. The subjects were able to identify correctly which of the treatments they had received.