“Opioids remain the drugs of choice for treating moderate to severe pain, although adverse effects limit their use. Therapeutic utility might be improved by combining opioids with other drugs to enhance analgesic effects, but only if adverse effects are not similarly changed.
Cannabinoids have been shown to enhance the antinociceptive potency of opioids without increasing other effects; this study examined whether the effectiveness of cannabinoids is altered in morphine-dependent monkeys.
Tolerance developed to the antinociceptive effects of morphine and cross-tolerance developed to cannabinoids under conditions that produced modest physical dependence.
Compared with the doses examined in this study, much smaller doses of opioids have antinociceptive effects when given with cannabinoids; it is possible that tolerance will not develop to chronic treatment with opioid/cannabinoid mixtures.”