What is the evidence that medical cannabis and cannabinoids are effective for the treatment of pain due to rheumatic diseases?
Marijuana is the dried leaves/flowers of the plant, Cannabis sativa. It contains over 460 different compounds of which 80 are classified as phytocannabinoids. Two of these (phyto)cannabinoids, tetrahydrocannabinol (THC) and cannabidiol (CBD), are most relevant to medicine. THC is the most psychoactive compound and has pain-relieving effects, whereas CBD has effects on immunologic function and can counteract some of the psychoactive effects of THC. CB1 and CB2 are the main receptors that both these cannabinoids bind to and exert their effects. Other receptors (TRPV1, GPR55) may also be important. CB1 is primarily found in the brain and responsible for the psychoactive effects, whereas CB2 is found peripherally throughout the body and thought to modulate pain and inflammation. The scientific basis to support medical cannabis/cannabinoids is based on the evidence that endocannabinoids are endogenous ligands derived locally from the breakdown of phospholipids during inflammation and tissue injury that bind to CB2 to dampen inflammation. However, to date there is little evidence that medical cannabis/cannabinoids significantly modulate pain and inflammation in any of the rheumatic diseases.