The Benzodiazepine Receptor Antagonist, Flumazenil Does Not Block Clinical Effects of Delta-9-tetrahydrocannabinol

Fifteen normal volunteer men were given intravenous doses of 2 mg of delta-9-tetrahydrocannabinol (THC) and 3 were given doses of 0.5 mg. Five, 15 and 30 minutes later, they were given intravenous doses of the benzodiazepine receptor antagonist, flumazenil. Doses of this compound ranged between 0.1 and 3.2 mg for single doses and 0.7 and 6.4 mg for total doses, being increased progressively with each successive subject, until dose-ranging was completed in 10 subjects. After that 5 subjects were given doses of 2 mg of THC on two occasions, followed by either doses of 3.2 or 6.4 mg flumazenil or placebo, administered under blind conditions. Three subjects were treated with 0.5 mg doses of THC followed by 3.2 mg of flumazenil or placebo under similar conditions. Despite doses of the antagonist which would have been adequate to reverse the effects of substantial doses of benzodiazepines, little ameliorative action was observed on the level of intoxication or the degree of conjunctival injection, two quite reliable clinical indicators of THC action. The benzodiazepine receptor does not seem to play any significant role in the psychoactive actions and conjunctival injection produced by THC.