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

  • Canadian Study
  • MS Society Funded

Summary: Cognitive dysfunction affects 40-80% of people with multiple sclerosis (MS), leading to greater difficulty in maintaining work, sustaining relationships, and pursing leisure activities. This study investigates whether withdrawal from cannabis use results in cognitive improvements.

Background: An estimated 20% of people living with MS use cannabis multiple times per week and over many years. The reasons for using cannabis vary by individual as it can provide relief from pain, spasticity, anxiety, depression, insomnia or a combination of these factors. With increased access to cannabis following legalization in Canada, it is anticipated that cannabis use may increase and therefore, important to gain more clarity on its potential benefits and side effects.

Study: A total of 40 people with MS who were long-term frequent users of cannabis following their MS diagnosis participated in the study. Half of the participants were asked to continue their normal use, and the other half were asked to abstain from use (withdrawal group). The participants in each group were assessed at the beginning of the study (baseline) and then 28 days later for their cognitive function. The precise composition and potency of the cannabis used by the participants varied across participants (38.5% of participants in the study used medically prescribed cannabis). Additionally, the cannabinoid detected in participants was predominantly tetrahydrocannabinol (THC).

Results: 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.

Impact: 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

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