Cannabis worsens cognitive function in patients with multiple sclerosis (MS), reported investigators recently in the journal Neurology.1 Marijuana has been used to relieve the pain and spasticity associated with MS; however, the results of this study show that the drawbacks may outweigh the purported benefits.
The study included two groups of patients with MS: 25 cannabis users and 25 nonusers. The average duration of cannabis use was 26 years. Seventy-two percent of users reported smoking marijuana daily, 24% reported weekly use, and one person reported bi-weekly use.
Both groups were administered the Minimal Assessment of Cognitive Function in MS battery of neuropsychological tests, the Hospital Anxiety and Depression Scale, and the Structured Clinical Interview for the DSM-IV Axis I Disorders.
The cannabis users scored significantly worse than nonusers on measures of information processing speed, working memory, executive functions, and visuospatial perception. They were also twice as likely as nonusers to be classified as globally cognitively impaired. No difference was found between the groups on measures of anxiety, depression, and psychiatric disorders.
"Given that about 40% to 60% of MS patients have problems with cognitive function to begin with, any drug that may add to this burden is cause for concern," said study author Anthony Feinstein, MPhil, MD, PhD, with Sunnybrook Health Services Center and the University of Toronto in Ontario, Canada.
1. Honarmand K, Tierney MC, O'Connor P, Feinstein A. Effects of cannabis on cognitive function in patients with multiple sclerosis. Neurology. 2011;76:1153-1160.