The major lignan in chaparral, known as nordihydroguaiaretic acid (NDGA) is a potent antioxidant and was thought by some scientists to be a potential cancer treatment. In a rat study, NDGA and a leaf extract of a South American subspecies of chaparral were found to exert an antitumor effect. However, one report suggests that NDGA may stimulate further growth of tumors in cancer patients. Clinical trials, therefore, are still needed to establish whether chaparral is a safe and effective treatment for people with cancer.
Other reported effects for chaparral include anti-inflammatory properties as well as antimicrobial actions in test tubes. These actions have note been established in human clinical trials