New Findings on Marijuana's Ability to Treat Chronic Pain

The majority of people who purchase medical marijuana report that they are treating chronic pain associated with injuries, neuropathies, or arthritis. The sensation of chronic pain is often due to the presence of inflammation in the effected tissues. My laboratory demonstrated that stimulation of cannabinoid receptors contributes to the anti-inflammatory effects of medical marijuana. In contrast, there are only anecdotal reports that cannabidiol (CBD) has anti-inflammatory effects. This is likely because CBD cannot stimulate cannabinoid receptors. CBD does modestly reduce anxiety; this action at serotonin receptors might reduce some cognitive aspects of the pain.

A pair of recent studies investigated whether there are other chemicals in the cannabis plant that contribute to the pain-relieving actions of medicinal marijuana. Their purpose was to identify molecules in the cannabis plant that might be useful treatments for chronic pain without producing psychoactive side effects. Many older patients report that the psychoactive effects are unpleasant. One study examined the anti-inflammatory properties of oil extracts of the leaves while a second study examined the anti-inflammatory chemicals found in an aqueous extract of cannabis roots.

The oil-soluble chemicals in cannabis leaves and stems include the alkaloids, flavonoids, stilbenoids, various fatty acids, cannabinoids, and terpenofenoids. These molecules have antifungal, anti-inflammatory, anti-bacterial, and psychotropic effects. In contrast, aqueous extracts of cannabis roots contain very low levels of the psychoactive molecule THC, consistent with the low psychotropic potential of this part of the plant.

The aqueous extract of the roots of C. sativa contained detectable levels of tetrahydrocannabiorcolic acid, cannabisatavine, cannabichromenic acid, and anyhydrocannabisatavine. The recent study using mice demonstrated that the aqueous extract of the C. sativa root exhibited an anti-inflammatory effect that was due to the reduction of vascular extravasation and the inhibition of migration of inflammatory cells (primarily leukocytes), without effects on the central nervous system.

The second study evaluated the anti-inflammatory properties of an oil extract from cannabis flowers. The oil extract contained CBD and THC (the two most abundant cannabinoids) as well as the monoterpenes (alpha-Pinene, Camphene, beta-Myrecene and D-Limonene) and sesquiterpenes (beta-Caryophyllene, alpha-Bergamotene, alpha-Humelene, Humulene epoxide II, and Caryophyllene oxide).

The oil extract of cannabis flowers markedly suppressed the release of the pro-inflammatory cytokine TNF-alpha as well as many other indicators of inflammation. The oil extract also significantly reduced the level of edema in injured tissues. These data likely underlie why arthritis patients find medicinal marijuana effective.

It was once thought that the cannabis plant contained no aqueous-soluble chemicals that have therapeutic use. This is obviously not the case. There is much more to learn about the contents of the cannabis roots.

Dr. Gary L. Wenk serves on the Ohio Governor's Medical Marijuana Advisory Committee.