PC-SPES (Botanic Lab, Brea, CA) is a combination of eight herbal therapies with activity against prostate cancer, both in vitro and in vivo. Studies in human prostate cancer cell lines demonstrate significant dose-dependent decreases in cellular viability after exposure to extracts of PC-SPES. Clinical studies suggest that PC-SPES can reduce specific antigen levels in both androgen-dependent and androgen-independent prostate cancer patients. Toxicity is mild, thought there is an approximately 5% risk of thromboembolic events with treatment. Although PC-SPES has apparent estrogenic activity, controversy exists over the exact mechanism of its effects.