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Am Fam Physician. 2018;98(8):online

Clinical Question

What are the benefits and harms of cannabinoids?

Bottom Line

This umbrella review found a modest benefit of cannabinoids for the treatment of neuropathic pain; a greater benefit for the treatment of spasticity and nausea and vomiting; and substantial harms. The studies were extremely heterogeneous in terms of the comparators, dose, duration, and outcome measures, so any conclusions should be taken with a grain of salt. (Level of Evidence = 1a–)


This is an umbrella review, which is a systematic review of systematic reviews. The authors did a broad search and identified 31 systematic reviews of the benefits and harms of cannabinoids, each with at least two randomized controlled trials. The topics addressed included pain, nausea and vomiting, spasticity, and adverse events. Individual outcomes were addressed in between two and 28 studies and in 44 to 2,737 patients. Challenges of this approach include a variety of populations, interventions, doses, and comparators, as well as the challenge of masking patients to treatment assignment. Most meta-analyses found a modest benefit, approximately 0.4 to 0.8 points, compared with placebo. Such a small benefit is unlikely to be clinically meaningful because we usually look for at least a 1-point improvement on a 10-point scale. Studies were moderately heterogeneous, with approximately one-half finding some benefit and one-half finding no benefit (intervention implementation = 43%). Benefit was generally greater in studies of neuropathic pain. Studies on the treatment of nausea and vomiting primarily included chemotherapy patients and those receiving palliative care (number needed to treat [NNT] = 3 to 7). There was significant heterogeneity. There was some evidence of benefit for treatment of spasticity as measured by the outcome of responder vs. nonresponder (NNT = 7 to 10), although the reductions in a 10-point spasticity score were modest (0.31 to 0.76). Adverse events such as feeling high, disorientation, and confusion were relatively common (number needed to treat to harm [NNTH] = 2 to 15), although psychosis was relatively rare. The NNTH to discontinue the medication was between 8 and 22.

Study design: Meta-analysis (randomized controlled trials)

Funding source: Unknown/not stated

Setting: Various (meta-analysis)

Reference: AllanGMFinleyCRTonJet alSystematic review of systematic reviews for medical cannabinoids: pain, nausea and vomiting, spasticity, and harms. Can Fam Physician2018;64(2):e78–e94.

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