Long-term consequences of medicinal cannabis use in people with multiple sclerosis (PwMS) are unknown. This study investigated whether PwMS using cannabis had lower resting brain glucose uptake (GU) and worse clinical test results compared with nonusers 

Positron emission tomography (PET), with the glucose analog [18F]-Fluorodeoxyglucose (FDG), has been used to investigate brain function in healthy and clinical populations. FDG-PET studies have shown that regular heavy alcohol use, cannabis, and other illegal drug use could lead to lower resting nervous system glucose uptake (GU). 

It has been suggested that lower brain GU may be responsible for some of the cognitive and physical impairments seen in these drug abuse populations. In PwMS, lower brain GU has been associated with clinical symptoms, such as fatigue, cognitive ability, and walking speed.

Brain GU may be an effective biomarker for the tracking of disease progression and disability in PwMS. How cannabis use affects brain GU in PwMS is unknown.

Sixteen PwMS, eight users, underwent clinical testing followed by [ 18F] -Fluorodeoxyglucose positron emission tomography / computed tomography imaging. 

Users had lower cognitive function test scores but performed similarly on the other clinical evaluations. Accounting for disease duration, resting brain GU was similar between the groups. 

Cognitive dysfunction

The lower cognitive function was not associated with resting brain GU. Cognitive dysfunction may be a contraindication or consequence of cannabis use in PwMS.

This is the first investigation reporting resting brain GU of PwMS regularly using cannabis. Our main findings: Regular cannabis use does not result in lower resting brain GU in PwMS, balance and mobility were mostly similar between the groups, and PASAT scores were lower in cannabis users. Lower PASAT scores were not associated with lower GU.

This study did not detect any effects of regular cannabis use on resting brain GU, which has been shown to be a marker for clinical disability. The lower cognitive performance in PwMS currently using cannabis is consistent with the current literature. However, the mechanisms of this dysfunction have yet to be elucidated.

Based on our preliminary findings, it is unlikely that resting brain metabolic activity/GU account for the differences in cognitive ability, assessed by the PASAT measure.

As stated in a previous review, there is a crucial need to determine the effects of commercially available cannabis products to increase the knowledge of risks and benefits of cannabis use in PwMS.