Multiple sclerosis and cannabis - A cognitive and psychiatric study

Background: A significant minority of patients with multiple sclerosis (MS) use cannabis, yet no study has examined the possible effects on mentation. Here, we report the emotional and cognitive correlates of street cannabis use in patients with MS. Methods: A sample of 140 consecutive patients with MS were interviewed with the Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) Axis I disorders (SCID-IV) from which details of cannabis use were recorded. Cognition was assessed using the Neuropsychological Battery for MS supplemented with the Symbol Digit Modalities Test (SDMT), an index of information processing speed, working memory, and sustained attention. Results: Ten subjects (7.7%) were defined as current cannabis users based on use within the last month. Compared to non-cannabis users (n = 130), they were younger (p = 0.001). Each of the 10 current cannabis users was matched on demographic and disease variables to four subjects with MS who did not use cannabis (total control sample n = 40). Group comparisons revealed that the proportion of patients meeting DSM-IV criteria for a psychiatric diagnosis was higher in cannabis users (p = 0.04). In addition, on the SDMT, cannabis users had a slower mean performance time (p = 0.006) and a different pattern of response compared to matched controls (group x time interaction; p = 0.001). Conclusions: Inhaled cannabis is associated with impaired mentation in patients with multiple sclerosis, particularly with respect to cognition. Future studies are required to clarify the direction of this relationship.