MS patients who used cannabis performed worse on cognitive tests and were twice as likely to be cognitively impaired | Research

The takeaway

Among 50 MS patients, cannabis users performed significantly worse on processing speed, working memory, executive function, and visuospatial perception, and were twice as likely to be globally cognitively impaired.

Read this if you have MS and use cannabis, and want to understand the potential cognitive trade-offs.

2x more likely to be globally cognitively impaired among cannabis-using MS patients

What the researchers found

Researchers compared 25 MS patients who used cannabis to 25 matched MS non-users using a comprehensive neuropsychological battery designed specifically for MS.

Cannabis users performed significantly worse on information processing speed, working memory, executive functions, and visuospatial perception. They were twice as likely to be classified as globally cognitively impaired.

Importantly, there were no differences in depression, anxiety, or lifetime psychiatric diagnoses between the groups, meaning the cognitive differences were not explained by mood disorders.

The authors noted that whatever subjective benefits patients derived from cannabis (pain or spasticity relief) should be weighed against these cognitive costs, particularly since MS already causes cognitive deterioration.

Why it matters

Since MS already impairs cognition, the finding that cannabis compounded these deficits was clinically significant for the many MS patients using cannabis for symptom relief.

The numbers in context

25 cannabis users vs 25 non-users. Cannabis users twice as likely to be globally cognitively impaired. Significantly worse on processing speed, working memory, executive function, and visuospatial perception. No mood differences between groups.

How the study worked

Cross-sectional study of 50 MS patients (25 cannabis users, 25 non-users). Minimal Assessment of Cognitive Function in MS battery, Hospital Anxiety and Depression Scale, and SCID-I administered. Group-matching and regression controlled for age, sex, education, premorbid intelligence, disability, and disease characteristics.

What this study cannot tell us

Cross-sectional design cannot determine whether cannabis caused the cognitive deficits or whether more cognitively impaired patients were drawn to cannabis use. "Street cannabis" was used, not standardized pharmaceutical products. Small sample size.

How to read the evidence

Well-matched cross-sectional study with comprehensive neuropsychological battery but small sample size and inability to establish causation.

When this study was published

Published in 2011. Research on cannabis and MS cognition has continued to develop.

The bigger picture

This study raised important questions about the risk-benefit balance of cannabis use in MS, where symptom relief must be weighed against potential cognitive harm in a population already vulnerable to cognitive decline.

Questions still open

Would pharmaceutical cannabis products (like Sativex) produce the same cognitive effects? Do the cognitive costs outweigh the symptom benefits for individual patients?

Common questions

Does cannabis worsen thinking problems in MS?

In this study, MS patients who used cannabis performed significantly worse on cognitive tests. However, the study could not determine whether cannabis caused the impairment or whether patients with worse cognition were more likely to use cannabis.

Should MS patients avoid cannabis?

This study suggested that cannabis users with MS had worse cognitive outcomes. The authors recommended weighing subjective benefits (pain, spasticity relief) against potential cognitive costs, particularly since MS already affects cognition.

Read the original research

Effects of cannabis on cognitive function in patients with multiple sclerosis.

Neurology, 76(13), 1153-60

View on PubMed ↗Publisher’s paper ↗

Citation

Honarmand, Kimia; Tierney, Mary C; O'Connor, Paul; Feinstein, Anthony. (2011). Effects of cannabis on cognitive function in patients with multiple sclerosis.. Neurology, 76(13), 1153-60. https://doi.org/10.1212/WNL.0b013e318212ab0c