Why is Capsaicin injection not used instead of nerve surgeries for pain?
High concentration capsaicin kills c & a-delta nerve fibers permanently or at least long term. This has been known for 30 years. But capsaicin is only used in creams and patches, and not for injecting direcly into nerves, and people resort to nerve surgeries like nerve blocks, razor-damaging nerves, or rhizotomy to cut the nerve partially or fully. All of these options affect not just pain functions, but overall sensory functions. On the other hand, capsaicin destroying c & a-delta fibers just affects pain. So why is no one interested in capsaicin injection as an option before cutting nerves?
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1 Expert Answer
Sandra K. answered • 06/04/25
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Capsaicin is effective as a topical application for pain relief because it cannot penetrate deeply into muscles. In addition, because of its composition and injection, capsaicin would cause additional pain. Last, drugs seek a receptor to function, and according to research, capsaicin inhibits this function.
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Stanton D.
Actually, it is used already, or at least a synthetic analog (to ensure patentability, I suppose!) for osteoarthritis of the knee. Since cartilage is poorly vascularized, it sticks around a while, targets only sites furnishing osteoarthritic pain, and doesn't scoot off to other parts of the body faster than it can be metabolized. By the way, there are analogs of capsaicin that are far (like 1 million x) "hotter", b/c they covalently, irreversibly bind to the receptor sites. Now, as to your implied therapeutic use, it would be difficult to target only the particular nerves you wanted, and also pain processing is so tied into CNS function (consider phantom limb pain, for instance). -- Cheers, -- Mr. d.09/03/20