Injection of synthetic chilli pepper extract – trans-capsaicin – reduces arthritis knee pain

A single injection of trans-capsaicin, a synthetic treatment based on the extract that gives chilli peppers their spicy taste, was found to lower osteoarthritis knee pain and have a good safety profile in a study reported in Arthritis and Rheumatology.

A total of 172 people aged 45 years to 80 years with knee osteoarthritis were split into groups: single injection of placebo; 0.5mg trans-capsaicin; or 1mg trans-capsaicin.

Three months after the injection, people who had the trans-capsaicin were more likely to have reduced knee pain. Improvements were maintained at six months for people who had the higher dose. Treatment-related adverse events were similar between the placebo group and the 1mg trans-capsaicin group.

“Trans-capsaicin works in a way that is different to existing therapies – it does not have to be continuously present in the joint to produce a significant, long lasting analgesic effect,” researcher Dr Randall Stevens, explains to Healio Rheumatology. “Patients with moderate to severe pain from knee osteoarthritis, including moderate to severe radiographic damage, with a body mass index up to 45kg/m2 and have failed prior treatment, can, from a single 1mg [trans-capsaicin] injection, have substantial reduction in pain and 49% to 60% improvement in knee stiffness and function. This has onset by the second day and a duration of benefit of up to six months, all while having a side effect profile that is similar to placebo.”

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