Chaparral is a plant prevalent in the desert regions of Mexico and southwest United States with a long medicinal history. Native Americans used extracts and preparations from this plant to treat skin sores, diabetes, cancer, venereal disease, tuberculosis, colds, and rheumatism. The aqueous extract, known as chaparral tea, has been employed for the treatment of kidney and gallbladder stones.

A phase II clinical trial found chaparral to be ineffective as an anticancer agent ⁽⁹⁾. In another small retrospective study, low intake of chaparral tincture (<10%) did not cause adverse effects ⁽³⁾, but the association between length of exposure and risk is not known.

Nordihydroguaiaretic acid (NDGA), the active compound isolated from chaparral, has been investigated for its biological effects. In preclinical studies, it demonstrated antioxidant ⁽¹²⁾, anticancer ^{(2) (13) (19) (20)}, antiviral ⁽²¹⁾, antiparastitic ⁽²²⁾, neuroprotective ⁽¹⁴⁾ and renoprotective ⁽¹⁵⁾ properties. It also had a protective effect against diet-induced metabolic function ⁽²³⁾. However, studies in humans are quite limited. One pilot in patients with relapsed prostate cancer suggested NDGA was reasonably well tolerated and affected increases in PSA doubling time, but it was also associated with transaminitis in some patients ⁽¹⁶⁾.

Several cases of reversible and irreversible liver damage ^{(4) (7) (8) (17)} have been associated with chaparral and products containing chaparral. NDGA, formerly employed as a food additive in low concentrations, has been removed by the FDA from its “Generally Recognized as Safe” (GRAS) substances list ⁽¹⁾. Also Masoprocol, a topical cream containing NDGA for the treatment of actinic keratoses, was withdrawn from the US market in June 1996 ⁽¹⁸⁾.

Chaparral is an ingredient in black salve, which is promoted as an alternative cancer treatment.