Cannabis: An MS researcher's perspective

I have been interested in the effects and side effects of smoked cannabis for many years. Having been involved in multiple sclerosis research and patient care, I’ve had a significant minority of my patients report smoking cannabis on a regular basis – indicating that it helps with pain, spasticity or both.

In a disease without a cure, such as MS, good symptom management is important and if indeed smoked cannabis is proving helpful, then these potential benefits need to be weighed against the possible side effects of further cognitive dysfunction.

Forty to sixty percent of people with MS will have cognitive difficulties. These problems relate to working memory, speed of information processing and problem-solving abilities. To date my research group in Toronto has published two papers showing that people with MS who smoke cannabis are likely to experience even greater cognitive challenges. This suggests that cannabis may, and I stress may, have cognitive dysfunction as an important side effect. The most recent of my two published papers was a very careful comparison of cognitive abilities in a group of 25 people with MS who smoked cannabis and a demographically and a disease-matched group of 25 people with MS who did not. The rates of cognitive impairment in the MS cannabis group were twice what they were in the non-cannabis smoking group – particularly related to a further delay in speed of information processing and greater difficulties with problem-solving or executive function.

I have used the word “may” above because to date our sample sizes have been modest. We are currently embarked on a third cannabis study where the cognitive results appear thus far to replicate the earlier ones. We have incorporated functional MRI in this new study to see how the brains of cannabis smokers differ from those of people with MS who do not smoke when it comes to solving a particular cognitive problem. The data for this aspect of the study has not yet been completely analyzed. 

I believe that it is important for researchers to look carefully at the side effects and potential benefits of cannabis. To date, we have no clear figures on how many people with MS may smoke or ingest cannabis. Within the broader Canadian general population we know that 15-20 percent will have used cannabis at some point in their lives. Recent data from the general population show quite convincingly that should a person start using cannabis as a teenager and continue use on a regular basis into mid-life then cognitive problems are likely to arise. We do not yet have that same degree of certainty with respect to people with MS.

There are many uncertainties with respect to cannabis and only good research will be able to clarify them. Given that three separate studies from my lab have arrived at the same conclusions, the advice that I give my patients is as follows: should you be contemplating using cannabis because you believe it will help your pain or spasticity or both, do so with an understanding that it might cause cognitive problems or further aggravate existing cognitive problems. Like many situations in medicine the physician and the patient must weigh up the benefits and risks of any intervention. Should one side of the equation outweigh the other, then the clinical course becomes clearer. In time, as more data come in from my lab and those of my colleagues, the uncertainties that currently exist will almost surely give way to a clearer set of do’s and don’ts when it comes to cannabis treatment guidelines.
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Anthony Feinstein, PhD

Anthony Feinstein, MPhil, PhD, MRCPsych, FRCPC, is a behavioral scientist, professor of Psychiatry at the University of Toronto and Chair of the Medical Advisory Committee of the MS Society of Canada.