Male patients with chronic radicular nerve pain—pain that radiates from the spine to the thigh, calf, and occasionally the foot—who were treated with tetrahydrocannabinol (THC), the psychoactive ingredient in marijuana, reported more pain relief than those who were administered a placebo. Brain scans also showed a decrease in activity in areas of the brain associated with processing pain. These are the results of a small randomized, double-blind, placebo-controlled trial, published online in Neurology on September 5.
Pain Ratings
To learn more about the pain-relieving effect of THC, a team of researchers at the Tel Aviv Medical Center in Israel recruited 15 male participants whose average age was 33 and who had chronic lumbar radicular pain. The researchers excluded women based on previous evidence that menstrual hormone fluctuations may affect pain sensitivity.
Before starting treatment, participants underwent a clinical evaluation and were asked to rate their pain on a scale of 0 to 100, with 0 being the lowest and 100 being the highest. All patients reported medium to high pain with a rating of 40 or above.
Brain Scans
Participants also underwent six-minute functional magnetic resonance imaging (fMRI) brain scans to assess the connections between various areas of the brain. The researchers asked patients to keep their eyes closed and relax, but not fall asleep.
At the start of the study, participants received either an average of 15 milligrams of THC oil or placebo oil under their tongues. An hour after treatment, participants ranked their pain severity. Another two hours after treatment, they underwent a second brain scan. One week later, participants came back for a second visit and those who received placebo were given THC and vice versa.
THC Improved Pain Ratings
Based on participants’ responses one-hour after treatment, researchers reported that THC significantly reduced participants’ pain severity compared to placebo. On average, the THC group rated pain levels at 35 compared to 43 for the placebo group.
Less pain coincided with reduced connectivity between the anterior cingulate cortex and other pain-related areas of the brain on participants’ fMRI scans. The researchers believe THC may alleviate pain by disrupting the signals between these pain processing pathways.
More Research Is Needed on THC
The researchers say the findings warrant larger studies to determine whether a combination of THC and cannabidiol—the non-psychoactive ingredient in marijuana known for its anti-inflammatory effects—is more beneficial than THC alone.
Future studies should also include women and test the effects of THC on other chronic pain conditions to find out whether the pain-relieving effect works for other types of pain.