MS patients who quit cannabis for 28 days showed significant cognitive improvement on every test | Research

The takeaway

Multiple sclerosis patients who stopped using cannabis for 28 days showed significant improvements in memory, processing speed, and executive function, confirmed by both neuropsychological testing and functional brain imaging.

Cannabis users with MS, people concerned about cannabis and cognitive function, and anyone considering a tolerance break.

Every cognitive test improved significantly (P < 0.0001) after just 28 days off cannabis

What the researchers found

After 28 days of abstinence, the withdrawal group performed significantly better on every cognitive measure (P < 0.0001 for all) compared to the continuation group. fMRI showed the abstinent group completed more trials correctly with faster reaction times and significantly increased brain activation in frontal, caudate, and cerebellar regions.

Why it matters

This is one of the few controlled studies directly measuring what happens when chronic cannabis users stop. The dramatic improvements across every cognitive domain after just 28 days suggest that cannabis-related cognitive deficits in MS patients are largely reversible.

The numbers in context

40 MS patients, frequent long-term cannabis users. Withdrawal group improved on every cognitive index (P < 0.0001). fMRI: more correct trials (P < 0.012), faster reaction time (P < 0.002). Increased bilateral inferior frontal gyri, caudate, and cerebellar activation (P < 0.001). THC was the predominant cannabinoid consumed.

How the study worked

Controlled study of 40 MS patients who used cannabis at least 4 days/week for years. Patients were divided into cannabis continuation and withdrawal groups with assessments at baseline and day 28 including neuropsychological battery, structural MRI, functional MRI, and urine testing for compliance.

What this study cannot tell us

Small sample size (40 patients). Non-randomized group assignment (odd-even selection). Only 28 days of abstinence studied. One patient in withdrawal group failed abstinence. Cannot separate acute withdrawal effects from genuine cognitive recovery.

How to read the evidence

Strong: controlled design with matched groups, objective compliance monitoring, and convergent neuropsychological and neuroimaging evidence.

When this study was published

Published in 2019 in Brain.

The bigger picture

Cognitive dysfunction already affects 40-80% of MS patients. Adding cannabis to that burden is measurable and, importantly, reversible. This provides concrete information for patients weighing the symptom-relief benefits of cannabis against its cognitive costs.

Questions still open

Would cognitive improvements continue beyond 28 days? Could lower-dose or CBD-predominant cannabis provide symptom relief without the cognitive penalty? Do these findings extend to cannabis users without MS?

Common questions

Does quitting cannabis improve thinking?

In this study of MS patients who used cannabis at least 4 days per week, stopping for 28 days produced significant improvements in memory, processing speed, and executive function. Brain imaging confirmed increased activity in relevant brain regions.

Are cannabis-related cognitive effects permanent?

This study suggests they are not. After 28 days without cannabis, MS patients showed significant improvement on every cognitive test. The matched group that continued using showed no such improvement, confirming the changes were due to stopping cannabis.

Read the original research

Coming off cannabis: a cognitive and magnetic resonance imaging study in patients with multiple sclerosis.

Brain : a journal of neurology, 142(9), 2800-2812

View on PubMed ↗Publisher’s paper ↗

Citation

Feinstein, Anthony; Meza, Cecilia; Stefan, Cristiana; Staines, Richard W. (2019). Coming off cannabis: a cognitive and magnetic resonance imaging study in patients with multiple sclerosis.. Brain : a journal of neurology, 142(9), 2800-2812. https://doi.org/10.1093/brain/awz213