MS, Cannabis & Cognitive Function

Anthony Feinstein, MD, PhD. gave the lecture - MS, Cannabis and Cognitive Dysfunction: Insights from Brain Imaging, to a standing-room only crowd at the opening presentation for the Consortium for MS Centers annual meeting in Indianapolis. He is in the Department of Psychiatry at the University of Toronto, and his research into this topic was funded by the National MS Society of Canada.

Dr. Feinstein began by tracing the roots of the drug back to the 9th century and took his audience through a timeline of cannabis use and its forms. One form was in the 19th century here in the US when it was combined with morphine and capsicum to be used as a pain killer. Well into the 20th century, cannabis was recognized and used by the medical field for its analgesic properties. “Cannabis has a long powerful lineage of medicinal use,” Dr. Feinstein said.

He then delivered a short course on Cannabis 101, and helped the uninitiated understand the plant, the various uses and some of the different language associated with cannabis. Dr. Feinstein outlined the effects of inhaled (smoked) cannabis, listing it has a rapid absorption rate, and it affects the brain usually under 30 minutes; but it also is almost gone for the high effect within 2-4 hours. There are residual chemicals from cannabis that will remain in the system for several weeks.

The statistics on cannabis use in the general population are telling - cannabis is used all over the world and it is estimated that 3.3-4.4% of people in the age range of 15-64 have tried cannabis at least one time. In North America, that rate increases to 10.5% and over 14% of Canadians over the age of 15 have smoke cannabis.

Cannabis studies are hard to perform because of inconsistency in the drug, drug delivery and other factors that might not be controlled. It is difficult to clearly know the frequency of use, the potency of the particular cannabis and the length of time a person may have been inhaling cannabis. Dr. Feinstein clearly stated more than once that his study is just preliminary and there is so little data on the use that the challenge is now for his colleagues to do further studies.

By looking at four studies and analyzing MRI images where available, Dr. Finestein told the audience there is demonstrated cognitive decline among people with MS who regularly smoke cannabis, and shared MRI images that back up his findings. For this study, Dr. Feinstein focused solely on cognitive function and how it might be affected by regularly smoking cannabis. He said there are a number of people who might benefit from its use for pain and spasticity and that is a separate set is questions and issues.

Here is what is known about MS and the use of cannabis, according to his presentation:

  • Approximately 40% of people with MS have used cannabis; the majority of it was smoked as opposed to being ingested. Over half of this number report their first use of cannabis was after their MS diagnosis.
  • The majority of people with MS who smoke cannabis are men, and they usually have a higher rate of disability.

Somewhere between 40-70% of people with MS have cognitive problems, which can be concerning. These problems include but aren’t limited to information processing speed, working memory, visual-spatial memory and executive function. In the studies, Dr. Feinstein notes cognition for people with MS – the ability to perform basic functions tests - decreases after smoking cannabis. In comparison tests, they found significant differences between people with MS and people without MS in the results. He went on to share MRI images that show these differences. He also shared MRI results showing white and gray matter changes from smoking cannabis. Whether these changes are permanent is not known, and he said there need to be studies to see if the brain can reverse the damage is the use of cannabis is discontinued.

The results of the limited studies to date are a mixed bag and this is the list of conclusions Dr. Feinstein shared in his presentation:

  • Cannabis further compromises cognitive function in some MS patients
  • Cannabis here refers to street cannabis and not Sativex, Marinol or Cesamet
  • No evidence that cannabis compromises mood or anxiety.
  • No evidence of psychosis.
  • The potentially deleterious cognitive effects should be weighed against benefits in other areas (pain, spasticity, urinary problems etc).

If you would like to read the articles he refers to in his presentation, I have included that list at the end of this article.

What I found interesting in the entire conversation was the apparent shift in the thinking of the medical community toward even having a public discussion regarding cannabis. Dr. Feinstein shared “I started with an anti-cannabis bias, but now I listen to my patients and I just tell them they should be aware the drug could cause possible cognitive problems. Like any other drug, they need to be aware of potential side effects,” and he added he knows it has value for patients who live with serious spasticity and/or pain.1-11

Wishing you well,


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This article represents the opinions, thoughts, and experiences of the author; none of this content has been paid for by any advertiser. The team does not recommend or endorse any products or treatments discussed herein. Learn more about how we maintain editorial integrity here.

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