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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