Multiple Sclerosis Society of Canada

Funded Research

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

Year Awarded: 2015

Term: 3 years

Funding Amount: $282,227

Affiliation(s): Sunnybrook Health Sciences Centre

Province(s): Ontario

Researcher(s): Dr. Anthony Feinstein

Hot Topics: Cannabis

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: In Progress

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