New information is available to multiple-sclerosis patients thinking of smoking marijuana to help deal with their symptoms.

On February 28, the Multiple Sclerosis Society of Canada issued a medical-update memo, which calls attention to a recent study that indicates “street” marijuana could be harmful to an MS patient’s cognitive functions, such as memory and thinking.

The report is coauthored by Toronto-based doctors Omar Ghaffar and Anthony Feinstein and its findings were published in the February 13 online edition of the clinical journal Neurology.

Speaking to the Straight from Toronto’s Sunnybrook Health Sciences Centre, Feinstein said that the study was significant because many patients with MS already show signs of cognitive impairment. Cannabis use seemed to aggravate that impairment, according to the study’s findings.

The study was carried out with 140 clinic attendees, 10 of which smoked cannabis frequently. Each individual who smoked was paired with four patients who did not, and a cognitive function test was carried out.

“We don’t want people to read too much into it because of the small sample size,” Feinstein cautioned, “but certainly, the cognitive result was quite impressive.”

In one particular test, the study found that MS patients who smoked marijuana were about 50 percent slower in completing the test—which consisted of matching numbers with symbols—than those who did not.

Feinstein noted that the study only looked at marijuana users who had obtained their drugs from sources outside of Canada’s medical-marijuana distribution system, and could not be applied to patients who had been prescribed cannabis.

In August 2007, Straight.com ran a health feature that presented anecdotal evidence on the benefits of smoking marijuana for MS patients.

MS is a disease that attacks the nervous system in the brain and spinal cord. Researchers believe it to be an auto-immune disease, meaning the body’s immune system has turned on itself and is actually causing the damage. Primary treatments for MS try to manipulate or control the immune system to stop it from attacking the nervous system.

Feinstein and Ghaffar’s report is available on Neurology’s website for US$20.