The actual definition of arthritis is: ‘a disease that causes painful inflammation and stiffness of the joints’ and there are over a hundred types of arthritis and related conditions including Osteoarthritis (OA), Rheumatoid Arthritis (RA), Juvenile Arthritis (JA) and Gout. OA is the most prevalent form of arthritis affecting around 27 million people in the US and almost 9 million people in the UK 1 & 2. In comparison, RA affects around 1.5 million Americans and about 400,000 people in the UK. It is also important to note that women are two to three times more likely to develop RA and are also more likely to develop OA than men are.
As discussed in the previous article, the science of cannabinoids and their reduction of inflammation is now well documented, with various cannabinoid-receptor dependent and independent pathways having been identified that directly influence inflammation. Due to the role inflammation plays in arthritic conditions this has resulted in many people across the globe resorting to cannabis or cannabis-based medicines to help alleviate their arthritic pains. But does the science support its use?
Studies performed on animal models of arthritic diseases tend to provide results that demonstrate a therapeutic effect, reducing pain and increasing mobility. One such study in 2015 compared the relationship between CB2 receptors and OA. Normal mice were compared with mice that had been genetically altered to not have CB2 receptors. This study showed that the OA was more severe in the mice with the genetic deletions (no CB2 receptors) and they also demonstrated that, in the normal mice, a CB2-selective agonist (a substance that binds specifically to the CB2 receptor) reduced the severity of OA in the whole joint 3.
Another study produced this year (2020) researched the effect of CBD on arthritis, firstly in human and mice cell cultures, followed by administration of CBD to dogs with arthritis. The testing on cell cultures corroborated previous research that showed CBD’s ability to reduce the production of inflammatory molecules and immune cells linked to arthritis. The administration of CBD to dogs with arthritis produced benefits in 90% of the dogs in the study, this was identified through observation of the animal’s gait and mobility, as well as with blood tests, and liver and kidney function tests. Interestingly the benefits were noticed two weeks after CBD administration had been stopped 4. The study chose to focus on dogs because experimental evidence shows that arthritic conditions in dogs are more appropriate to human arthritis than other animal models.
In a study on Collagen-Induced Arthritic (CIA) mice, which is a condition induced in mice to study RA, it was found that injecting 5mg/kg per day of CBD showed a potent anti-arthritic effect in CIA. Similar results were obtained with an oral dose of 25mg/kg per day of CBD 5. These effects are attributed to the combined immunosuppressive and anti-inflammatory actions of the cannabinoid.
Human studies evaluating the efficacy of anti-arthritic cannabinoids have also been performed. One randomised control study from 2005 showed that the administration of Sativex (a cannabis-based medicine, containing equal levels of THC and CBD) resulted in a significant analgesic (pain relieving) effect in RA sufferers 6. Another paper, produced in 2016, tested the efficacy of a synthetic cannabinoid, WIN55,212-2 (WIN), on 28 RA patients and 56 OA patients. The patients were administered with either a low or high dose of WIN. The low doses appeared to reduce inflammation via TRP channels without activating CB receptors, but in high doses WIN also activates CB1 and CB2 receptors as well which enhanced the anti-inflammatory and analgesic qualities 7. The study suggests that administration of WIN directly to a joint is an attractive arthritis therapy to be explored in the future.
Evidence for cannabinoid’s (both phyto- and synthetic) effectivity against arthritis is consistent, but also must be evaluated further. Many studies are focused on mice or rat models of arthritis and so there must be a concerted effort to study their effects in humans in greater detail. Studies need to be prolonged and include more patients to more accurately determine the long-term effects of cannabinoid administration as a therapeutic agent against various arthritic diseases. The potential is clearly there though!
Written by Joseph Wardle, MSc, BSc.