Capsaicin is an active alkaloid in hot peppers. It has been successfully used to reduce pain in herpes zoster, diabetic neuropathy and post-mastectomy pain syndrome (Sandford & Benes 2000). It works as an inhibitor of substance P.
Topical capsaicin was used to treat radicular post-SCI pain for 1-2 weeks (Sandford & Benes 2000). Patients showed improvement in pain and 2 of the 8 patients were still improved for over two years.
There is level 4 evidence (from one case series study: Sandford & Benes 2000) that topical capsaicin reduces post-SCI radicular pain.