Herbal dietary supplements (HDS) are widely used in complementary, alternative, and integrative medicine, but data on attitudes, behavior, safety, and efficacy are lacking. Using mixed methods, we administered an online survey to

1,000 breast cancer survivors to investigate HDS practices and perceptions and performed in vitro studies assessing the efficacy and toxicity of actein, a bioactive component of the HDS black cohosh (Actaea racemosa). Among cancer survivors, curcumin, flaxseed, and green tea were reported as the most frequently used HDS. Many subjects increased HDS intake after diagnosis and sought web-based information on HDS. In human breast cancer (MCF-7) and liver (HepG2/C3A) cell lines, actein had anti-proliferative and anti-estrogenic effects and did not exhibit hepatotoxicity or affect the action of tamoxifen and raloxifene.