Marijuana Chemical Chills Out Brain's Pain Threshold

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One of the active ingredients in Cannabis sp., or marijuana, may help patients endure pain, although it doesn’t block out the sensation as do pain-killers derived from poppies, such as morphine. University of Oxford doctors captured images of the brain on THC that showed reduced activity in sections associated with the emotional response to pain.

Test subjects were given a pill containing tetrahydrocannabinol (THC), one the strongest active chemicals in the Cannabis plant. To test their reaction to pain, a lotion with capsaicin was applied to their legs. Capsaicin is the chemical which give jalapenos their fiery kick. The study participants were given a brain scan using a magnetic resonance imaging (MRI) machine.

“The participants were asked to report the intensity and unpleasantness of the pain: how much it burned and how much it bothered them,” said lead author Michael Lee of the University of Oxford in a press release. “We found that with THC, on average people didn't report any change in the burn, but the pain bothered them less.”

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The MRI scan showed reduced activity in two areas associated with pain. One, the anterior mid-cingulate cortex, has been correlated in previous research to the emotional reaction to pain. The other, the right amygdala, has been associated with reducing the sensation of unpleasantness.

Patients experienced different levels of response to the THC, and the reaction of the amygdala may explain this, suggested the study authors. Observations of the amygdala may help doctors predict which patients will receive the most benefit from THC as a medicine.

“We may in future be able to predict who will respond to cannabis, but we would need to do studies in patients with chronic pain over longer time periods,” Lee said. “Our small-scale study, in a controlled setting, involved 12 healthy men and only one of many compounds that can be derived from cannabis. That's quite different from doing a study with patients."

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"My view is the findings are of interest scientifically but it remains to see how they impact the debate about use of cannabis-based medicines," said Lee. "Understanding cannabis' effects on clinical outcomes, or the quality of life of those suffering chronic pain, would need research in patients over long time periods.”

IMAGE:

A cannabis bud (Horsma / Hamppuforum, Wikimedia Commons)

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