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Dose-dependent Effects of Smoked Cannabis on Capsaicin-induced Pain and Hyperalgesia in Healthy Volunteers

Background:Although the preclinical literature suggests that cannabinoids produce antinociception and antihyperalgesic effects, efficacy in the human pain state remains unclear. Using a human experimental pain model, the authors hypothesized that inhaled cannabis would reduce the pain and hyperalgesia induced by intradermal capsaicin. Methods:In a randomized, double-blinded, placebo-controlled, crossover trial in 15 healthy volunteers, the authors evaluated concentration–response effects of low-, medium-, and high-dose smoked cannabis (respectively 2%, 4%, and 8% 9-&dgr;-tetrahydrocannabinol by weight) on pain and cutaneous hyperalgesia induced by intradermal capsaicin. Capsaicin was injected into opposite forearms 5 and 45 min after drug exposure, and pain, hyperalgesia, tetrahydrocannabinol plasma levels, and side effects were assessed. Results:Five minutes after cannabis exposure, there was no effect on capsaicin-induced pain at any dose. By 45 min after cannabis exposure, however, there was a significant decrease in capsaicin-induced pain with the medium dose and a significant increase in capsaicin-induced pain with the high dose. There was no effect seen with the low dose, nor was there an effect on the area of hyperalgesia at any dose. Significant negative correlations between pain perception and plasma &dgr;-9-tetrahydrocannabinol levels were found after adjusting for the overall dose effects. There was no significant difference in performance on the neuropsychological tests. Conclusions:This study suggests that there is a window of modest analgesia for smoked cannabis, with lower doses decreasing pain and higher doses increasing pain.