Cat's claw (Uncaria tomentosa) is made from the inner bark of a Peruvian vine and has been used by indigenous people for centuries to treat a variety of conditions. Its most widely promoted use is to enhance immune function, particularly the function of macrophages, which are cells that engulf invading germs. The plant may also possess antioxidant properties that help prevent toxins from lodging in tissues. Cat's claw, also called uña de gato, may increase a person's CD4+ count, as well. One small study that used the herb to treat people with HIV was done before HAART (highly active antiretroviral therapy) was available. The study showed small increases in the CD4+ counts of those taking cat's claw, and those increases rose slowly over a long period of time (at least four to six months). So far, one manufacturer of cat's claw has used the results of this study in its promotional literature. These results have not, however, been published in a medical journal. Although cat's claw may be useful against some types of cancers, more recent test-tube studies suggest that it may actually weaken cell-mediated immunity - the part of the immune system already damaged in people with HIV. For this reason, some researchers are beginning to question the use of cat's claw in HIV-positive people.
Cat's claw is available in capsules, powders, tinctures and as a highly concentrated extract. Because it's an endangered plant, the government of Peru has restricted its collection. This reality has increased the possibility that it may be replaced with other plants in some products. Unfortunately, some of the plants most commonly substituted for cat's claw suppress the immune system.
Traditionally used as a contraceptive and for urinary tract infections, cat's claw has no reported side effects, but women who are pregnant or wish to become pregnant should avoid it. The herb is processed in the body by the same enzymes used by many antiretroviral drugs, including protease inhibitors. Although there have been no reported cases of increased drug side effects associated with the use of cat's claw, the potential risk exists.