Cat's claw (Uncaria tomentosa) is a woody vine that grows in the Peruvian Amazon rain forest. Indigenous people have utilized this renowned plant for hundreds of years. Modern research has identified a group of constituents known as indole alkaloids that have been found to enhance macrophage activity in animal studies. Planetary Formulas Cat's Claw uses only the inner bark of the aboveground vine, which preserves the root for future growth.