Effects of Δ⁹-tetrahydrocannabinol (THC), cannabidiol (CBD), and THC/CBD mixtures on fentanyl versus food choice in rhesus monkeys

Daily methocinnamox treatment dose-dependently attenuates fentanyl self-administration in rhesus monkeys

Opioid use disorder and opioid overdose continue to be significant public health challenges despite the availability of effective treatments. Methocinnamox (MCAM) is a novel, long-acting opioid receptor antagonist that might be an effective treatment for opioid use disorder (i.e., preventing relapse and overdose). In nonhuman primates, MCAM selectively blocks the positive reinforcing effects of mu opioid receptor agonists, including heroin, fentanyl, and its ultra-potent analogs (e.g., carfentanil) with a single administration of MCAM being effective for up to two weeks. Because treatment of opioid use disorder would involve repeated administration of a medication, MCAM was studied in rhesus monkeys (3 males and 2 females) responding under a fixed-ratio self-administration procedure for a range of doses of fentanyl (0.000032-0.1 mg/kg/infusion). The fentanyl self-administration dose-effect curve was determined before and during treatment with progressively increasing daily doses of MCAM (0.001-0.1 mg/kg) given subcutaneously 1 h before the session. MCAM dose-dependently shifted the fentanyl dose-effect curve rightward and then, at larger doses, downward. The largest treatment dose of MCAM (0.1 mg/kg/day) shifted the curve more than 120-fold rightward with monkeys receiving doses much larger than the likely lethal dose of fentanyl with no adverse effect or observable change in behavior. This study demonstrates that MCAM reliably and dose-dependently decreases fentanyl self-administration and prevents opioid overdose, with no evidence of adverse effects over a broad dose range, further supporting the potential therapeutic utility of this novel antagonist.

Impact of Δ9-Tetrahydrocannabinol and oxycodone co-administration on measures of antinociception, dependence, circadian activity, and reward in mice

Oxycodone is commonly prescribed for moderate to severe pain disorders. While efficacious, long-term use can result in tolerance, physical dependence, and the development of opioid use disorder. Cannabis and its derivatives such as Δ9-Tetrahydrocannabinol (Δ9-THC) have been reported to enhance oxycodone analgesia in animal models and in humans. However, it remains unclear if Δ9-THC may facilitate unwanted aspects of oxycodone intake, such as tolerance, dependence, and reward at analgesic doses. This study sought to evaluate the impact of co-administration of Δ9-THC and oxycodone across behavioral measures related to antinociception, dependence, circadian activity, and reward in both male and female mice. Oxycodone and Δ9-THC produced dose-dependent antinociceptive effects in the hotplate assay that were similar between sexes. Repeated treatment (twice daily for 5 days) resulted in antinociceptive tolerance. Combination treatment of oxycodone and Δ9-THC produced a greater antinociceptive effect than either administered alone, and delayed the development of antinociceptive tolerance. Repeated treatment with oxycodone produced physical dependence and alterations in circadian activity, neither of which were exacerbated by co-treatment with Δ9-THC. Combination treatment of oxycodone and Δ9-THC produced CPP when co-administered at doses that did not produce preference when administered alone. These data indicate that Δ9-THC may facilitate oxycodone-induced antinociception without augmenting certain unwanted features of opioid intake (e.g. dependence, circadian rhythm alterations). However, our findings also indicate that Δ9-THC may facilitate rewarding properties of oxycodone at therapeutically relevant doses which warrant consideration when evaluating this combination for its potential therapeutic utility.

Oxycodone Self-Administration in Female Rats is Enhanced by ∆9-tetrahydrocannabinol, but not by Cannabidiol, in a Progressive Ratio Procedure

Epidemiological evidence suggests that the legalization of cannabis may reduce opioid-related harms. Preclinical evidence of neuropharmacological interactions of endogenous cannabinoid and opioid systems prompts further investigation of cannabinoids as potential therapeutics for the non-medical use of opioids. In these studies female rats, previously trained to self-administer oxycodone (0.15 mg/kg/infusion) intravenously in 6 h sessions, were allowed to self-administer oxycodone after exposure to cannabidiol (CBD) and Δ9-tetrahydrocannabinol (THC) by vapor inhalation and THC by injection (5.0-20 mg/kg, i.p.). Self-administration was characterized under Progressive Ratio (PR) and Fixed Ratio (FR) 1 schedules of reinforcement in 3 h sessions. THC decreased IVSA of oxycodone in a FR procedure but increased reward seeking in a PR procedure. CBD decreased the IVSA of oxycodone in the FR but not the PR procedure. The results are consistent with an anti-reward effect of CBD but suggest THC acts to increase the reinforcing efficacy of oxycodone in this procedure.