Capsaicin has been used to treat pain for a very long time. Before it was used in Western medicine, indigenous peoples of the Americas used hot peppers as medicine. Today, it is found in creams and ointments, patches and powders, all designed to help alleviate mild to moderate and even severe pain. How does it work, though? What’s the correlation between “substance P” and capsaicin?
The Supposed Action of Capsaicin on Substance P
Initially, researchers thought that the mechanism of action was a depletion of substance P by capsaicin. In the body, substance P is a chemical that is responsible for helping to communicate pain signals to the brain. A reduction in the amount of substance P in the affected area treated with capsaicin indicated that capsaicin’s effectiveness was due to its ability to reduce the amount of substance P, and therefore reduce the sense of pain in the body by curtailing pain-related signals to the brain.
It’s now thought that the reduction of substance P by capsaicin is not the actual mechanism of action, but a correlating reaction to something else. According to a study published by the National Institutes of Health, the real mechanism of action for capsaicin is not a reduction of substance P, but a “defunctionalization” of nociceptor fibers in the treated area.
The study states, “…experimental and clinical studies show that depletion of substance P from nociceptors is only a correlate of capsaicin treatment and has little, if any, causative role in pain relief. Rather, topical capsaicin acts in the skin to attenuate cutaneous hypersensitivity and reduce pain by a process best described as defunctionalization of nociceptor fibers.”
With that being said, while the new study points out that defunctionalization occurs and is a more likely result of using capsaicin to treat pain topically, there has not been a concrete determination that this is in fact its actual mechanism of action, and many medical professionals still point to the reduction of substance P by capsaicin as the best explanation for the pain relief experienced by patients when using creams and patches.
The Big Question – Does It Work?
For most people suffering from pain, the question is not concerned so much with the depletion of substance P by capsaicin, but the overall effect of topical creams and patches. Do they work? The answer is yes. Whether the depletion of substance P is the cause of the pain relief, or simply a side effect created by defunctionalization of nociceptor fibers, patients do experience pain relief when using products containing capsaicin.
Many different types of pain can be successfully treated with these products, including muscle strains and sprains, muscle soreness, pain in scar tissue, herpes lesion pain, cluster headaches, lower back pain and more. Higher dosage patches (8%, rather than .25%) have been developed for use with patients suffering from severe neurologic pain, as well, although these are available by prescription only and must be applied by a physician, rather than the patient.