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 discovered that cat's claw contains a group of indole alkaloids, shown in animal studies to enhance macrophage function. Planetary Formulas Cat's Claw uses only the inner bark of the aboveground vine, which preserves the root for future growth.