Cannabis in Pain and Arthritis: A Look at the Evidence
On Thursday, June 12, 2014 — day 2 of the — Dr. Mary-Ann Fitzcharles took the podium to discuss the use of medicinal marijuana in rheumatologic diseases. Dr. Fitzcharles is Associate Professor of Medicine in the Division of Rheumatology at McGill University in Montreal, and her talk was part of a symposium looking at the possibility of repurposing old or established analgesics for rheumatic diseases.
Fitzcharles began her talk with a historical look at cannabis use. The plant was first used in Europe and Asia around 5000 years ago, at which time scientists believe it contained very little tetrahydrocannabinol (THC), the primary psychoactive substance in today’s marijuana. Eventually, more THC-heavy strains were propagated, and the ancient Chinese began using the plant medicinally around 2700 years ago. “Queen Victoria used cannabis for her menstrual cramps,” Fitzcharles commented.
She then posed the question of why we have an endogenous cannabinoid system in the first place, before reviewing the correct dogma among experts. It’s thought that our cannabinoid system is involved in maintaining homeostasis, particularly in terms of stress, sleep, and modulation of pain. Furthermore, although they are often thought of for their neuro- and psychoactive effects, cannabinoid receptors are actually fairly ubiquitous throughout the body. They’re found on cells of the joints, bone, skin, and immune system, as well as on neurons.
Preclinical work in animals has found cannabinoids to be effective in nearly every acute pain model tested, likening them to some opioids in terms of their analgesic effects. Rodent models of arthritis demonstrate increased endocannabinoids in the spinal cord and upregulation of both cannabinoid receptor subtypes, CB1 and CB2. A recent study reported at the European Calcified Tissue Society Congress 2014 found that mice with destabilized knee joints had 40% more cartilage degeneration if they were deficient in these CB2 receptors. A study in humans suggests the presence of cannabinoid receptors on the synovia. So it appears that the endocannabinoid system has relevance to rheumatology.
However, with the good comes the bad, particularly in terms of brain function. Too much cannabinoid exposure can worsen memory, affect the reward system (and therefore have addiction implications), and impair cognition.