You probably know someone who has arthritis. According to the CDC, 54 million adults in the U.S. have been diagnosed with arthritis by a doctor. Arthritis is characterized by the inflammation of joints, which leads to pain and swelling. Perhaps surprisingly, it is a leading cause of disability in the U.S., which is why there is interest in exploring the use of cannabis to treat arthritis.
One of the most common types of arthritis is rheumatoid arthritis (RA), which, in addition to being an inflammatory disease, is also an autoimmune disease. The body’s own immune cells accumulate in the synovium (the tissue that lines joints) and release proteins that promote inflammation and the degradation of tissue.
There are two major issues that RA patients have to deal with — inflammation caused by the body’s own immune response against itself, and the subsequent pain as cartilage and bone are degraded and the joints become deformed.
Most treatments, such as non-steroidal anti-inflammatory drugs (NSAIDS) are symptomatic and used to manage pain and inflammation. Other treatment options include disease-modifying anti-rheumatic drugs (DMARDs) to slow progression of disease, as well as surgical intervention. However, there is accumulating evidence for the role of the endocannabinoid system in RA, which suggests that cannabinoids might be an effective treatment for RA.
The endocannabinoid system can likely mediate RA in multiple ways. Cannabinoid receptor type 1 (CB1) is found at the nerve terminals in both the central and peripheral nervous system. As a result, activation of CB1 has a significant effect on neuronal function. For example, activation of CB1 receptors located in neurons that are responsible for the transmission of pain can reduce the sensation of pain.
CB2 receptors, and to some extent CB1, are expressed in various cell types that are related to RA, including immune cells, and regulate the activity of these cells. For example, activation of CB2 in T-cells inhibits the proliferation of T-cells as well as the release of pro-inflammatory proteins. In RA, the expression of both CB1 and CB2 receptors, as well as of the endocannabinoids that activate them, is increased, suggesting the endocannabinoid system may be attempting to modulate the development and progression of RA by influencing both pain perception and autoimmune response.
In a 2014 study, scientists inhibited the degradation of endocannabinoids in a mouse model of RA. This resulted in a decrease in inflammation and pain in a CB1-dependent manner, suggesting that the endocannabinoid system can be harnessed to reduce inflammation and pain in joints.
Given the potential role of the endocannabinoid system in RA, there is increasing interest in pursuing cannabis as a potential therapy for RA. However, the current scientific evidence for cannabis as a treatment for RA is lacking. Hopefully, with the increased legalization of marijuana, we will continue to learn more about its potential therapeutic applications.