Marijuana (Cannabinoids)

Side effects of medical cannabinoids

Researchers from McGill University in Montreal reviewed the evidence.

First, the details.

  • Safety studies of medical cannabinoids published over the past 40 years were reviewed.
  • After excluding articles on recreational cannabis, 31 studies (23 randomized controlled trials and 8 observational studies) of medical cannabis use were analyzed.

And, the results.

  • In the 23 randomized controlled trials, the duration of cannabinoid exposure was about 2 weeks (range 8 hours to 12 months).
  • 4779 side effects were reported.
  • 97% were not serious.
  • Among 164 serious side effects, the most common included relapse of multiple sclerosis (13%), vomiting (10%), and urinary tract infection (9%).
  • The rate of nonserious side effects was higher among those assigned to medical cannabinoids vs controls.
  • The rates of serious adverse events did not differ between the groups.
  • Dizziness was the most commonly reported nonserious side effect (16%) among people exposed to cannabinoids.

The bottom line?
The authors concluded, “Short-term use of existing medical cannabinoids appeared to increase the risk of nonserious adverse events.”

By comparison, “The risks associated with long-term use were poorly characterized… High-quality trials of long-term exposure are required to further characterize safety issues related to the use of medical cannabinoids.”

6/17/08 21:14 JR

Hi, I’m JR

John Russo, Jr., PharmD, is president of The MedCom Resource, Inc. Previously, he was senior vice president of medical communications at, a complementary and alternative medicine website.