Multiple sclerosis patients who smoke marijuana were more likely to have a history of a mental illness and also performed worse on a test of their mental processing speed and working memory, according to results of a community-based study.
The data "provide the first evidence of the injurious effect of inhaled cannabis on the mentation of patients with MS," the authors wrote in Neurology.
Ascertaining the effect of cannabis use in MS patients is important because cannabis often is used as a therapeutic agent in the disease, and MS is "by itself a cause of neuropsychological impairment in 40%-65% of patients," wrote Dr. Omar Ghaffar and his colleague, Dr. Anthony Feinstein, both of the Sunnybrook Health Sciences Centre, Toronto, and the University of Toronto.
The researchers looked at 140 consecutive, community-dwelling MS patients seen at an outpatient clinic in Toronto. Three-fourths were women. The disease was relapse-remitting in 82 patients, secondary progressive in 49 patients, and primary progressive in 9 patients (Neurology 2008 [Epub doi:10.1212/01.wnl.0000304046.23960.25]).
Overall, 10 subjects reported current cannabis use (use of inhaled marijuana purchased on the street in the past month). Users and nonusers differed significantly in age (users had a mean age of about 36 years, vs. nonusers, whose mean age was 44.5 years, P = .001). There were no other differences with respect to disease, duration, disability, education, or gender.
"Since age is a factor that could potentially affect cognition independent of cannabis use, the 10 current cannabis users were each age-matched to 4 subjects who did not use cannabis [total control sample n = 40]," wrote the authors. Subjects were then evaluated using the Structured Clinical Interview for DSM-IV Axis I Disorders; the Hospital Anxiety and Depression Scale; and several cognitive assessments. …