can cannabis replace opioids

Researchers performed a systematic review of available studies to investigate whether cannabis can be used to replace opioids in patients receiving methadone maintenance therapy.

Cannabis has been a popular topic in the media over the past couple of years with the push for, and subsequent legalization of the drug. Recent discussions have mainly been focused on the distribution of the drug and the potential health benefits of cannabis use. One particular topic of interest has been in the use of cannabis to help people suffering from opioid use disorder. Opioid use disorder is a serious problem that has many negative health-related and social consequences associated with it.

Currently, the most common treatment used for opioid use disorder is methadone maintenance therapy. This treatment involves the controlled administration of the drug methadone, in combination with various forms of psychological support. Among patients receiving this treatment, the use of cannabis is quite high.

A group of researchers at McMaster University wanted to investigate whether this cannabis use had any evident benefit to those receiving treatment for opioid use disorder. The researchers performed a systematic review, published in CMAJ Open, of existing research on cannabis use in relation to methadone maintenance therapy. They specifically wanted to look at whether “patients using cannabis during methadone maintenance therapy have lower rates of opioid use during therapy” and whether “cannabis use improves treatment retention in opioid use disorder”.

In total, the researchers assessed 23 studies in their systematic review, with 12 being related to cannabis use and continued use of opioids during methadone treatment, and the other 11 looking at cannabis use and adherence to methadone treatment. In terms of the link between cannabis use and opioid use, the researchers found that from the studies they looked at, there was no evident connection between the use of cannabis and the continued use of opioids. Meaning that the use of cannabis during methadone maintenance therapy did not result in patients being any more or less likely to continue taking opioids. In regard to treatment retention, the studies the researchers looked at were unable to yield any conclusive results.

From their findings, the researchers noted that it seemed like the use of cannabis had no effect on the outcomes of methadone treatment. But they did note that the overall quality of the data they had to work with was not the greatest. The studies they used were all observational in nature, in that no manipulations of cannabis use to test for any potential effects on the treatment of opioid use disorder were performed. In addition, it was noted that “all the studies had a moderate or high risk of bias.” A common trend among the studies used was issues of imprecision and inconsistency in various aspects of how the studies were designed. The researchers also pointed out that the differences in findings between their review and other research could likely be as a result of the way ‘cannabis use’ was determined for each person. In the studies they assessed, cannabis use was simply divided into one of two categories (e.g., no cannabis use or cannabis use, a certain threshold of cannabis use or less than that, etc.). They explain that categorization in that manner can hide significant associations from showing up in the results. Another main issue pertaining to the nature of the study designs was that any other potential factors that could have affected the outcomes of methadone treatment, such as multiple drugs being used during the same period of time as cannabis use and methadone treatment, were not accounted for.

Overall the researchers were unable to find conclusive evidence that cannabis use was able to reduce opioid use in patients receiving methadone maintenance therapy, or any evidence that patients were able to adhere to treatment longer if they were using cannabis. However, these results should be interpreted cautiously as a result of the concerns previously mentioned. The researchers acknowledge that further research is required to truly understand the effects of cannabis use on “treatment outcomes in patients with opioid use disorder”.


Written by Haritha Thevar, BSc



McBrien, H., Luo, C., Sanger, N., Zielinski, L., Bhatt, M., & Zhu, X. et al. (2019). Cannabis use during methadone maintenance treatment for opioid use disorder: a systematic review and meta-analysis. CMAJ Open, 7(4), E665-E673. doi: 10.9778/cmajo.20190026

Cannabis found not to be a substitute for opioids. (2019). Retrieved 23 November 2019, from

Methadone Saves Lives – Addiction Counsellors and Methadone Maintenance Treatment. (2019). Retrieved 23 November 2019, from

Image by M. Maggs from Pixabay



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