When medical cannabis is taken for chronic nerve pain, it may provide pain relief by reducing connections between the areas of the brain that process emotions and sensory signals, according to a study published in Neurology.
The study looked specifically at radicular pain, a type of nerve pain that radiates from the spine into the legs. Sciatica is a common form of radicular pain.
The component of cannabis examined in this study was tetrahydrocannabinol (THC), one of more than 100 cannabinoids found in the cannabis plant, and the one most commonly associated with producing a euphoric effect or 'high'.
"Pain is a complex experience that involves both the senses and emotions," said study author Haggai Sharon, MD, of the Sagol Brain Institute, Tel Aviv Medical Center in Israel.
"Our study results link pain relief from THC with a reduction in the connections between areas of the brain otherwise heavily connected, suggesting that THC may alleviate pain by disrupting signals between these pain processing pathways."
The study involved 15 men with chronic radicular nerve pain with an average age of 33. Women were excluded since hormone fluctuations during menstruation may affect pain sensitivity. All participants had medium to high radicular pain for over six months.
Before treatment, participants rated their pain levels and had brain scans with functional magnetic resonance imaging (fMRI) to look at the connections between various areas of the brain. Participants were then given treatment with THC.
For the first visit, nine participants were given an average of 15 milligrams of THC oil placed under the tongue and six were given placebo oil. One hour after treatment, participants were questioned again, and had another brain scan approximately two hours after treatment.
At least one week later, participants returned for a second visit and those who had the placebo now received the treatment, and vice versa.
Researchers found that THC reduces a person's pain when compared to placebo. On a scale of zero to 100, before taking medication, on average participants rated their pain levels at 53. After taking THC oil, they rated their pain levels at an average of 35 compared to an average of 43 for those who were given the placebo.
In addition, the more pain relief a person experienced, the greater the reduction of connections between the areas of the brain involved in processing pain.
"Interestingly, our results also show that the more connected the areas of the brain that process emotion and sensory prior to treatment, the greater the pain relief experienced when taking THC," said Sharon. "Larger studies are needed to confirm our findings."
Limitations of the study are that women were excluded and the number of participants was small. Also, this study looked only at THC. Future studies are needed to examine how other components of the cannabis plant, like cannabidiol (CBD), may be useful in relieving pain in combination with THC.
The study was funded by the Yahel Foundation and the Israeli Ministry of Science, Technology and Space.
Libat Weizman, Lior Dayan, Silviu Brill, Hadas Nahman-Averbuch, Talma Hendler, Giris Jacob, Haggai Sharon. Cannabis analgesia in chronic neuropathic pain is associated with altered brain connectivity. Neurology, 2018; 10.1212/WNL.0000000000006293 DOI: 10.1212/WNL.0000000000006293