Support your immune system and digestion with Source Naturals Cat's Claw! Cat's Claw (Uncaria tomentosa) is an herb that grows in the rain forests of the Peruvian Amazon where it has been used for centuries by the Native Peruvians. Recent research has discovered that its inner bark has unique active, alkaloid constituents that help support the body's immune system. Now used worldwide as a nutritional supplement, cat's claw is obtained without needless destruction of the plant, thereby protecting the delicate Amazon ecosystem.