Cannabis Users with MS Show Poorer Processing Speed and Working Memory | Research

The takeaway

Among 847 people with MS, cannabis users performed significantly worse on processing speed and working memory tests, even after controlling for age, education, disease duration, anxiety, and fatigue.

MS patients using cannabis, neurologists, cognitive rehabilitation specialists

30% of MS patients used cannabis; all showed poorer processing speed

What the researchers found

Cannabis users (n = 254) performed significantly worse than nonusers (n = 593) on the Symbol Digit Modalities Test (processing speed, p = 0.014). After adjustment, cannabis independently predicted poorer performance on SDMT, PASAT-3, and PASAT-2 (all p < 0.001), explaining 7-16% of variance.

Why it matters

People with MS already face cognitive challenges, particularly with processing speed. If cannabis use compounds these deficits, it is relevant information for patients using cannabis for symptom relief who may not realize the cognitive trade-off.

The numbers in context

847 patients; 254 cannabis users (30%); significant effects on SDMT (p = 0.014); SDMT, PASAT-3, PASAT-2 all p < 0.001 after adjustment; models explained 7-16% of variance.

How the study worked

Cross-sectional study of 847 consecutive MS patients administered the MACFIMS cognitive battery. Cannabis users (n = 254) compared to nonusers (n = 593) using MANOVA and multiple linear regression controlling for age, education, disease duration, anxiety, and fatigue.

What this study cannot tell us

Cross-sectional design cannot determine whether cannabis caused cognitive deficits or whether those with worse cognition are more likely to use cannabis. No information on cannabis type, potency, frequency, or mode of use. Recreational users only.

How to read the evidence

Large consecutive clinical sample with validated cognitive battery and adjusted analyses, but cross-sectional design limits causal inference.

When this study was published

2025 publication

The bigger picture

Cannabis is commonly used by MS patients for pain, spasticity, and sleep. This is the largest study to examine objective cognitive effects in this population. As cannabis potency increases and legalization expands, the cognitive impact in vulnerable neurological populations warrants attention.

Questions still open

Does the cognitive impact differ by cannabis potency or consumption method in MS patients?
Would longitudinal data show that cannabis use accelerates cognitive decline in MS?

Common questions

Does cannabis affect thinking in people with MS?

In this study of 847 MS patients, cannabis users scored significantly lower on tests of processing speed and working memory compared to nonusers, even after accounting for age, education, disease duration, anxiety, and fatigue.

Should people with MS avoid cannabis?

This study found an association between cannabis use and poorer cognitive performance in MS, but it cannot prove cannabis caused the deficits. MS patients using cannabis for symptom relief should be aware of potential cognitive trade-offs and discuss them with their neurologist.

Read the original research

Cannabis and Cognitive Function in Multiple Sclerosis: Findings From a Large Consecutive Clinical Sample.

European journal of neurology, 32(7), e70142

View on PubMed ↗Publisher’s paper ↗

Citation

Kever, Anne; Meza, Cecilia; Feinstein, Anthony. (2025). Cannabis and Cognitive Function in Multiple Sclerosis: Findings From a Large Consecutive Clinical Sample.. European journal of neurology, 32(7), e70142. https://doi.org/10.1111/ene.70142