In this issue of JFP, Weinstein and Worster provide a wealth of information about prescribing marijuana. Medical marijuana (Cannabis) is now legal in the majority of states, so it’s likely that some of your patients are using marijuana for symptom relief. For those physicians who elect to prescribe marijuana, reading this review will help you avoid harming patients while maximizing potential benefits.
I say “potential benefits” because the research evidence to support benefit for most conditions and symptoms is weak at best. In addition to the JAMA meta-analysis cited by Weinstein and Worster,1 several meta-analyses and systematic reviews published since January 2018 reach similar conclusions.2-4
Marijuana can provide significant relief from chemotherapy-induced nausea and vomiting, and it is effective in reducing intractable seizures in 2 rare pediatric seizure disorders. There may be some benefit for treatment of spasticity, and there may be some therapeutic value for relief of neuropathic pain, although the evidence is not strong. Interestingly, there is some preliminary evidence that cannabis can improve gastrointestinal symptoms in patients with Crohn's disease and ulcerative colitis.5,6
Why do people use marijuana as medicine? A meta-analysis found that pain (64%), anxiety (50%), and depression/mood (34%) were common reasons.7 People use marijuana for a plethora of other conditions and symptoms, which is reflected in the long list of “approved” conditions in most state medical marijuana laws. The problem I have with prescribing cannabis for non-neuropathic pain, anxiety, and depression is that there is no good randomized trial evidence of its effectiveness beyond a placebo effect (which is probably quite strong considering the psychotropic effects of marijuana). And, as Weinstein and Worster point out, there is evidence of increased mental health symptoms in chronic marijuana users.
Regardless of the scientific evidence, use of cannabis for symptom relief is unlikely to be a passing fad. Surveys show that about 70% of users believe they receive benefit from it.8 Therefore, it behooves us to be prepared to discuss the pros and cons of cannabis use with our patients—even if we decide not to prescribe it. Warn patients with anxiety and depression that it is unlikely to be effective and may make matters worse.
There is intense interest in medical marijuana and better research will likely change the way we use cannabis for medical purposes in the future. So, for now, our best approach is to stay informed as the research unfolds.