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

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.

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.

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.

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.

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.