Tildabeth Doscher, MD, MPH

The study by Socías and colleagues suggests that cannabis use can reduce the risk for fentanyl exposure and fentanyl overdose. As there is no randomization or control of the intervention (cannabis use), it is difficult to draw any conclusions. The authors suggest that use of cannabis is an intentional strategy to reduce opioid use by inferring this link based on other studies. In the current study, however, there was no assessment of whether cannabis was used intentionally by the participants as a strategy to reduce illicit opioid use.

The study’s location (Vancouver) introduces a potential confounder of legal availability of a safe injection site for opioid use. It is not reported how many participants in the study accessed legal, controlled opioids through this site. Individuals who use this site would not have fentanyl exposure for any use at that site. Therefore, it is possible that participants using opioids through the safe injection site also use cannabis at higher rates, and that lower exposure to fentanyl is driven by where and how opioids are obtained and used. It is hard to tell if Socías and colleagues would have gotten the same results if the study was conducted elsewhere, because there is a lot we do not know.

One predictor of overdose risk is prior overdose — this is not mentioned as a measured variable. Similarly, a predictor of cannabis use is prior history of cannabis use. There is an implicit assumption in the study that increased cannabis use acts as a substitution for opioid use, and therefore may result in less exposure to fentanyl. The idea of substance preference is not raised. There are people who get more of what they are looking for from using one substance over another and, hence, the use of cannabis may have had to do with choice rather than self-treatment of a primary opioid use disorder, as the study seems to suggest.

As with other studies, design flaws limit conclusions. It is always most important to recognize that association does not equal causation. The authors of this study repeat speculation about associations between cannabis use and opioid use and overdose risk, and they also note that other studies examining the evidence of the link between cannabis use and fentanyl exposure have found inconsistent findings. Such links need a stronger experimental design, and a more rigorous study such as a randomized clinical trial is needed before definitive conclusions can be drawn.

The study by Socías and colleagues also provides a cautionary tale of the problem of publishing a study that can give an impression of a positive finding by those who look at the literature mainly by reading abstracts. Many physicians, who often have limited time, skim through research literature. A cursory review could result in some concluding that since people who use cannabis use less fentanyl, it must be endorsing the use of cannabis. When we are looking at the illness of addiction, we must be careful when we start to advocate for treating the illness created by one addictive substance by the use of another addictive substance. We must guard against making a statement that one substance is “safer” than another when it comes to the illness of addiction. This mindset of not recognizing and/or minimizing potential harm perpetuates danger upon danger, which is how we got to the opioid crisis in the first place.

This is not to say that there is no room for the role of harm reduction. Fentanyl is deadly. Cannabis, in and of itself, is not, at least not in the immediate way that fentanyl is. It may well be that increased cannabis use leads to decreased illicit opioid use. This particular study does not demonstrate that and my experience as an addiction doctor working in outpatient clinics (prescribing both methadone and buprenorphine) and in inpatient rehabs is that cannabis use does not decrease opioid use. In fact, the disease of addiction is self-perpetuating and is fueled by adding one substance that leads to the illness to another that maintains the illness. I have not seen that cannabis use decreases the use of opioids among my clients.