Interaction of physostigmine and delta-9-tetrahydrocannabinol in man.

To investigate the hypothesis that delta-9-tetrahydrocannabinol (THC), the major psychoactive ingredient of marihuana, acts by interfering with cholinergic brain mechanisms, 0.75 to 1.25 mg of physostigmine, a centrally active cholinergic drug, was given intravenously to 5 normal volunteers who had ingested 20 to 40 mg of THC 2 hours earlier. Physostigmine decreased the degree of tachycardia and conjunctival injection produced by THC. The major psychologic effects of physostigmine were amplification of the lethargy and somnolence which occur late in the course of THC intoxication. We interpret the lack of physostigmine counteraction of the peak psychologic effects of THC as evidence against the hypothesis that THC acts predominantly by an anticholinergic mechanism.