Flavokawain B is a natural chalcone first isolated from extracts of kava roots. It induces apoptosis in androgen receptor-negative, hormone-refractory prostate cancer cell lines (IC50s = 32, 48, 6.2, and 3.9 µM for LAPC4, LNCaP, PC-3, and DU145 cells, respectively, treated for 48 hours), with increased expression of the proapoptotic protein Bim. Flavokawain B increases Bim expression and inhibits growth of DU145 xenografts in mice. It also increases Bim expression, promotes apoptosis, and induces cell cycle arrest in uterine leiomyosarcoma cells. However, flavokawain B is hepatotoxic, triggering oxidative stress, inhibiting NF-κB signaling, and activating MAPK pathways, culminating in HepG2 and L-02 cell death (LD50s = 15 and 32 µM, respectively).