Open-label pilot study of injectable naltrexone for cannabis dependence

Background: There are no FDA-approved pharmacotherapies for cannabis use disorders (CUD), despite the evaluation of numerous medications. Notably, chronic dosing of oral naltrexone decreases self-administration of cannabis in human laboratory studies.

Objectives: To test the feasibility of long-acting injectable naltrexone for the treatment of CUD, while obtaining preliminary safety and efficacy data.

Methods: Twelve adult participants (seven male) meeting DSM-IV-TR criteria for cannabis dependence enrolled into an 8-week, open-label pilot study conducted at an academic treatment research clinic. They received 380 mg intramuscular injections of long-acting naltrexone on study day 1 and at the start of study week 5. Outcome measures included percentages of study completers and participants who received the second injection, frequency of adverse events (AEs), and cannabis consumption measured by average daily grams, dollars, and using days per week as measured by timeline follow-back and urine oral delta-9-tetrahydrocannabinol (THC) concentrations.

Results: Of the 12 participants enrolled in the study, 9 completed the study and 6 received the second injection. There were no severe AEs but an unexpected AE led to the addition of supportive medications to the protocol. Number of cannabis use days per week significantly decreased over the course of the study (p = .001). Creatinine-corrected urine THC concentrations and average daily cannabis use per study week in grams and in dollars did not decrease over the course of the study.

Conclusions: Long-acting injectable naltrexone is a feasible intervention for CUD worthy of further study in a placebo-controlled, double-blinded randomized clinical trial.