Weizman L, Dayan L, Brill S, Nahman-Averbuch H, Hendler T, Jacob G, Sharon H. Cannabis analgesia in chronic neuropathic pain is associated with altered brain connectivity. Neurology 2019;91:e1285-e1294 (abstract)

Why was this study conducted?

There is a lot of interest in the ability of cannabis, particularly its main psychoactive substance Δ-9-tetrahydrocannabinol (THC), to relieve pain.  In this randomized, double-blind, placebo-controlled cross-over trial, researchers conducted functional magnetic resonance imaging (fMRI) of the brain before and two hours after sublingual administration of THC or a placebo.  Subjects were 15 men aged 27-40 years with chronic radicular neuropathic pain (i.e., pain due to inflammation or other irritation of a nerve root at its connection to the spinal cord).

What does this study add?

The study found patients’ subjective reporting of pain correlated with a reduction in connectivity between two parts of the brain associated with pain processing: the anterior cingulate cortex (ACC), which is involved in processing the affective aspects of pain, and the sensorimotor cortex, which plays a role in the sensory aspects of pain.  The authors suggest pain relief may occur because THC disrupts synchrony and integration between these two pain-processing pathways. In addition, THC may reduce activity in the dorsolateral prefrontal cortex (DLPFC). These findings suggest a neurologic explanation for the analgesic effects of THC.

Is there anything else I should know?

This was a small study (n=15) that only included men with a specific type of neuropathic pain. More research will be needed to validate these findings and determine whether they are applicable to women and other forms of pain.

Author Details

The latest scientific evidence on this topic was reviewed by the Centre's leadership team. This research summary is written by Corinne Hodgson, DHealth, assessed for accuracy by Co-Director Dr. James MacKillop, PhD, an expert in addictions and mental health research. There are no conflicts of interest. Questions regarding this piece should be directed to Dr. James MacKillop (jmackill@mcmaster.ca).

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