Hill KP. Medical marijuana for treatment of chronic pain and other medical and psychiatric problems, a clinical review. JAMA 2015;313(24):2474-83 Abstract

Why was this study conducted?

In the U.S., the Food and Drug Administration (FDA) has approved two synthetic cannabinoids in pill forms (dronabinol and nabilone) for the treatment of chemotherapy-induced nausea and vomiting or wasting associated with cancer or human immunodeficiency virus infection (HIV). To help practitioners uncertain of the benefits and risks of medical cannabis, the author found and analyzed a total of 40 randomized controlled trials (RCTs) using nabilone, dronabinol, nabiximol, or smoked cannabis.

What does this study add?

For chronic (lasting for over three months) and neuropathic (nerve-related) pain, the ten studies that compared a cannabis product to a placebo (an inactive substance used as a control) reported a significant decrease in pain but the one that compared it to an existing pain medication found the codeine medication was more effective. For multiple sclerosis (MS), five of the trials showed cannabis reduced spasticity (unusual muscle tightness, stiffness or paralysis), one showed no effect on spasticity but a decrease in episodes of incontinence, and six showed no benefits. No benefits were observed in the individual studies of Parkinson’s disease, Crohn disease, or amyotrophic lateral sclerosis (ALS). The one study of neurogenic symptoms such as numbness, tingling and muscle weakness found that compared to a placebo, cannabis was associated with significant decreases in pain and spasticity. The author summarizes five practical considerations healthcare providers need to address when deciding whether to prescribe medical cannabis and recommends that, as with any medication having significant adverse effects and potential for abuse, there should be close follow-up to monitor safety and efficacy.

Is there anything else I should know?

The author provides very useful summaries of medical cannabis laws in the U.S. as of March, 2015, and the 40 identified research studies. However, there was no attempt to rate the quality of the trials, the placebo conditions or to systematically capture information on adverse effects. The majority of the studies used synthetic cannabinoids in the form of pills or an extract spray; in only three (all for neuropathic pain) was the cannabis smoked.

Author Details

The latest scientific evidence on this topic was reviewed by the Centre's leadership team. This research summary is written by Corinne Hodgson, DHealth, assessed for accuracy by Co-Director Dr. Jason Busse, PhD, an expert in research methodology and pain. There are no conflicts of interest. Questions regarding this piece should be directed to Dr. Jason Busse (bussejw@mcmaster.ca).