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The effect of caffeine (300 mg/70 kg) on cognitive, perceptual and motor functions was investigated both alone and in combination with ethanol (0.75 g/kg) in 68 healthy student volunteers of both sexes. A test battery consisting of standing steadiness, simple and complex reaction time, manual dexterity, numerical reasoning, perceptual speed and verbal fluency was used. Placebos for both drugs were included. Caffeine was administered in decaffeinated coffee immediately after finishing drinking the alcoholic beverage. A peak plasma ethanol concentration of 92 +/- 4 mg/100 ml occurred at 40 min which was not modified by caffeine. Caffeine did not antagonise the ethanol-induced decrement in performance except in the reaction time tests. Caffeine alone caused a significant increase in body sway at 40 min.

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Summary1. After oral administration to mice, pethidine, A8-tetrahydrocannabinol (THC), A9-THC, a cannabis extract and cannabinol had a dose-dependent antinociceptive effect when measured by the hot-plate method. Cannabidiol was inactive at 30 mg/kg. A8-THC, A9-THC and pethidine did not differ significantly in potency, but A9-THC was 6 5 times more active than cannabinol. 2. After oral administration, three different cannabis extracts, A8-THC, A9-THC and morphine produced dose-dependent depressions of the passage of a charcoal meal in mice. A8-THC and A9-THC were equipotent and were about five times less potent than morphine. Cannabidiol was inactive up to 30 mg/kg. The effect of the three cannabis extracts on intestinal motility could be accounted for by their A9-THC content.3. The antinociceptive effect of pethidine and the effect of morphine on intestinal motility were antagonized by nalorphine whilst the effects of the cannabis extracts and the pure cannabinoids were not. 4. From these results it is concluded that although cannabis and the narcotics share several common pharmacological properties, the mode of action of each is pharmacologically distinct.

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