We’ve been prescribing medical marijuana for migraines and other painful conditions since it was legalized in the state of New York four years ago. While it does not seem to help most of our patients, it does benefit a significant minority. The benefits may include relief of pain, nausea, anxiety, and improved sleep. Various ratios of tetrahydrocannabinol (THC) and cannabidiol (CBD) produce different effects and often neither one alone is as effective as a combination of the two (so called entourage effect). Although marijuana is a very effective medicine for some patients, there is no good science to explain how it works, in what combination of ingredients and for what types of pain.
A very interesting study that sheds some light on the possible mechanism of action of THC was just published in a leading neurology journal, Neurology by Israeli researchers. They enrolled fifteen patients with chronic neuropathic pain in the leg (like sciatica) in a double-blind placebo-controlled crossover study. Nine patients were given THC in the first part of the study and placebo in the second and six were given placebo first and then THC. In addition to measuring the effect of THC on pain the researchers performed functional MRI (fMRI) scans before and after administering THC or placebo.
THC was significantly better than placebo at relieving pain and the fMRI scans showed THC-induced changes in the way pain may be processed in our brains. They found that THC produced a reduction in functional connectivity between the anterior cingulate cortex (ACC), a major pain-processing region that is rich in cannabinoid receptors and the sensorimotor cortex. This reduction correlated with the reduction in the subjective pain ratings after THC treatment, meaning that patients who did not have pain relief usually did not have a decrease in the connectivity between the two regions.
The study also showed that pretreatment functional connectivity between the ACC and the sensorimotor cortex positively correlated with the improvement in pain scores induced by THC, that is, the higher the positive functional connectivity at baseline, the more benefit was gained from THC administration.
The authors also commented that THC combined with CBD may have stronger pain-relieving properties. Hopefully, the researchers will figure out the best combination of THC and CBD, but it is possible that other ingredients in marijuana contribute to the therapeutic effects. This could be why some of our patients prefer products from one dispensary and not the other and why some find that the whole plant is more effective than THC with CBD in any ratio. Most patients also find that products made from different strains of marijuana plant (sativa vs indica) have different effects.
