CMAJ • June 17, 2008; 178 (13). doi:10.1503/cmaj.071178.
© 2008 Canadian Medical Association or its licensors
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Research

Adverse effects of medical cannabinoids: a systematic review

Tongtong Wang, MSc, Jean-Paul Collet, PhD MD, Stan Shapiro, PhD and Mark A. Ware, MBBS MSc

From the Departments of Epidemiology and Biostatistics (Wang, Collet, Shapiro), Anesthesia (Ware) and Family Medicine (Ware), McGill University, Montréal, Que.; the Centre for Healthcare Innovation and Improvement (Collet), Children's and Women's Health Centre, University of British Columbia, Vancouver, BC; and the Alan Edwards Centre for Research on Pain (Ware), McGill University, Montréal, Que.

Correspondence to: Dr. Mark A. Ware, Alan Edwards Centre for Research on Pain, Rm. E19.145, Montréal General Hospital, 1650 Cedar Ave., Montréal QC H3G 1A4; fax 514 934-8491; mark.ware{at}mail.mcgill.ca

Background: The therapeutic use of cannabis and cannabis-based medicines raises safety concerns for patients, clinicians, policy-makers, insurers, researchers and regulators. Although the efficacy of cannabinoids is being increasingly demonstrated in randomized controlled trials, most safety information comes from studies of recreational use.

Methods: We performed a systematic review of safety studies of medical cannabinoids published over the past 40 years to create an evidence base for cannabis-related adverse events and to facilitate future cannabis research initiatives. We critically evaluated the quality of published studies with a view to identifying ways to improve future studies.

Results: A total of 321 articles were eligible for evaluation. After excluding those that focused on recreational cannabis use, we included 31 studies (23 randomized controlled trials and 8 observational studies) of medical cannabis use in our analysis. In the 23 randomized controlled trials, the median duration of cannabinoid exposure was 2 weeks (range 8 hours to 12 months). A total of 4779 adverse events were reported among participants assigned to the intervention. Most (4615 [96.6%]) were not serious. Of the 164 serious adverse events, the most common was relapse of multiple sclerosis (21 events [12.8%]), vomiting (16 events [9.8%]) and urinary tract infection (15 events [9.1%]). The rate of nonserious adverse events was higher among participants assigned to medical cannabinoids than among controls (rate ratio [RR] 1.86, 95% confidence interval [CI] 1.57–2.21); the rates of serious adverse events did not differ significantly between these 2 groups (RR 1.04, 95% CI 0.78–1.39). Dizziness was the most commonly reported nonserious adverse event (714 events [15.5%]) among people exposed to cannabinoids.

Interpretation: Short-term use of existing medical cannabinoids appeared to increase the risk of nonserious adverse events. The risks associated with long-term use were poorly characterized in published clinical trials and observational studies. High-quality trials of long-term exposure are required to further characterize safety issues related to the use of medical cannabinoids.


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The adverse effects of cannabinoids: implications for use of medical marijuana
Louisa Degenhardt, MPsych(Cli and Wayne D. Hall, PhD
Can. Med. Assoc. J. 2008 178: 1685-1686. [Full Text] [PDF]



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L. Degenhardt MPsych(Cli and W. D. Hall PhD
The adverse effects of cannabinoids: implications for use of medical marijuana
Can. Med. Assoc. J., June 17, 2008; 178(13): 1685 - 1686.
[Full Text] [PDF]

eLetters:

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Cannanboids are relatively ineffective in pain relief.
Peter R. O'Loughlin
CMAJ, 20 Jun 2008 [Full text]