In contrast to the anecdotal reports of benefit with cannabis, this study from researchers at the University of Toronto in Canada uncovers the downside of street cannabis in patients with multiple sclerosis (MS).

First, the details.

  • Details of cannabis use in 140 consecutive patients with MS were recorded.
    • 10 of these patients had smoked marijuana as treatment for the disease.
  • Cognition (reasoning ability) was assessed using the Neuropsychological Battery for MS supplemented with the Symbol Digit Modalities Test (SDMT), an index of information processing speed, working memory, and sustained attention.

And, the results.

  • Marijuana smokers performed 50% slower on tests of information processing speed compared to MS patients who did not smoke marijuana.
  • There was also a significant association between smoking marijuana and emotional problems such as depression and anxiety.

The bottom line?
The authors noted that people with MS have higher rates of depression and suicide compared to the general population. “Since marijuana can induce psychosis and anxiety in healthy people, we felt it was especially important to look at its effects on people with MS.”

“This is the first study to show that smoking marijuana can have a harmful effect on the cognitive skills of people with MS,” said Dr. Anthony Feinstein. “This is important information because a significant minority of people with MS smoke marijuana as a treatment for the disease, even though there are no scientific studies demonstrating that it is an effective treatment for emotional difficulties.”

2/23/08 15:07 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.