Wang and colleagues performed a systematic review of safety studies of medical cannabinoids published over the past 40 years and found that short-term use appeared to increase the risk of non-serious adverse events.

Of all non-serious adverse events, dizziness was the most common (15.5%).

"We found that the rate of non-serious adverse events was 1.86 times higher among medical cannabinoid users than among controls," state the authors. "However, we did not find a higher incidence rate of serious adverse events associated with medical cannabinoid use." The authors note that 99% of the serious adverse events from randomized controlled trials were reported in only 2 trials, a fact the authors say suggests that more studies are required to further characterize safety issues.

In a related commentary, Dr. Louisa Degenhardt, Professor of Epidemiology, National Drug and Alcohol Research Centre, University of New South Wales, Sydney, Australia, states that, although the side effects of oral cannabis therapy appear to be minor in the short term, their longer-term effects, particularly in the setting of chronic illness, have yet to be studied.


Tongtong Wang MSc, Jean-Paul Collet PhD MD, Stan shapiro PhD, Mark A. Ware MBBS MSc, 'Adverse effects of medical cannabinoids: a systematic review', Canadian Medical Association Journal - Volume 178, Issue 13 (June 2008)

Louisa Degenhardt PhD MPsych(Clin, Wayne D. Hall PhD, 'The adverse effects of cannabinoids: implications for use of medical marijuana', Canadian Medical Association Journal - Volume 178, Issue 13 (June 2008)