Harpagoside is an iridoid glycoside compound primarily found in the plant Harpagophytum procumbens, commonly known as Devil's Claw. This plant has a history of traditional use in managing musculoskeletal pain and inflammatory conditions, particularly in African and European herbal medicine. Modern scientific interest has focused on harpagoside because of its demonstrated anti-inflammatory properties in preclinical studies. These studies indicate that harpagoside can inhibit the production of pro-inflammatory cytokines and mediators such as TNF-α and COX-2, which are implicated in tendon inflammation.

Clinical trials examining Devil's Claw extracts (standardized to harpagoside content) have shown some benefit in reducing pain and improving function in osteoarthritis and low back pain, but there is a lack of direct, high-quality evidence specifically for tendonitis. Most of the supportive data come from animal studies and in vitro experiments showing anti-inflammatory effects in tendon cells, rather than large randomized controlled trials in humans with tendonitis. Systematic reviews and meta-analyses acknowledge the anti-inflammatory potential of harpagoside, but generally call for more targeted research on tendon-specific conditions.

In summary, while there is scientific rationale and some supportive evidence for using harpagoside for inflammatory musculoskeletal conditions, the direct evidence for tendonitis is limited, resulting in a moderate evidence rating.