Coming off cannabis in MS: a longitudinal, cognitive and fMRI study

Start Term
End Term
Funding Amount
Sunnybrook Health Sciences Centre
Geographic Region(s) / Province(s)
Hot Topic(s)
Research Priorities
Cognition and mental health
Impact Goal(s)
Advance Treatment and Care


  • Almost one in five people with multiple sclerosis (MS) use cannabis. People with MS using cannabis to alleviate some of their symptoms have more extensive deficits generally involving information processing speed, working memory and executive function.
  • What is not known in MS is whether the cognitive and imaging changes in cannabis users are reversible with drug abstinence.
  • The research team will:
    • Examine if the negative cognitive effects of cannabis can be reversed if a subset of participants stop cannabis use compared to another group that continues to use cannabis.

Project Description:

Between 40% and 60% of people living with MS experience difficulties with their cognitive functioning. Cognitive impairment is associated with greater difficulty in securing a job, functioning socially and pursuing leisure activities. Almost one in five people with MS report using cannabis (marijuana) for symptom relief, most notably for pain and spasticity. However, new evidence indicates that smoking cannabis may worsen cognitive function in MS. What is not known, however, is whether these cognitive changes are reversible if a person with MS stops smoking cannabis. Dr. Anthony Feinstein and his team will pursue this question by performing cognitive testing and brain imaging on two groups of participants: one group will be instructed to stop using cannabis while the other will be allowed to continue, and both groups will be followed for 28 days. Preliminary data suggests that individuals with MS who abstain from cannabis use show less cognitive impairment. Overall, the results of this project will be important in educating people living with MS and physicians alike about the effects of cannabis on cognition.

Potential Impact: Results from this study will impact clinical practice in a significant way, health care providers will have a better grasp on the types of cognitive deficits, and changes in the brain associated with cannabis use and if these deficits are potentially reversible.

Project Status: Closed



October 30, 2019 - Understanding the effect of cannabis use on cognition (memory, processing speed and executive function) in people affected by MS

There were no differences between the two groups at baseline. On day 28, however the withdrawal group performed significantly better on every cognitive index. The withdrawal group showed better performance on tests of information processing speed, learning and memory (both visual and verbal), and executive function. Improvements in processing speed was matched by increases in cerebral activation as detected by functional MRI. Coming off cannabis was not associated with a significant worsening of symptoms and any withdrawal symptoms noted were transient and manageable.

This is the first study to demonstrate that frequent, long-term cannabis users can show significant cognitive improvements following drug abstinence. Critical variables that may reduce recovery of cognitive deficits following abstinence as seen in this study may include age of onset (e.g. cannabis use during adolescence when the brain is still developing) and duration of use (e.g. longer-term users prior to MS diagnosis). More studies such as these are needed to understand the benefits and side effects of cannabis use. Research study is published in the journal Brain - link

October 4, 2017- MS Society funded study explores the effects of cannabis on cognition in men and women with MS

Of the 140 individuals who participated in the study, 33 people used cannabis regularly. Of the 33 users that used cannabis, 14 were men and 19 were women. Irrespective of gender, cannabis users had lower processing speed compared to non-cannabis users. Interestingly, the researchers identified that men performed worse compared to women on visual and verbal memory functions as measured using the California Verbal Learning Test-II.

Overall, the study found that cannabis use among people with MS can have impacts on cognitive functioning, specially a negative effect on memory. This is particularly true for men as was found using certain tests of memory. There limitations of this study were that there were only 33 individuals who were sampled, which limited the comparison to 14 men and 19 women, and there was no information on the frequency of cannabis use (e.g. how many times per week, month, etc.) so it is unknown if greater or lesser use of cannabis impacts any of the cognitive assessments.

The MS Society advocates for all safe and efficacious treatment options to be available to people living with MS, and supports high quality research such as Dr. Feinstein’s work which provides valuable information about medical marijuana that help patients, their families, and healthcare teams make appropriate treatment decisions.