A pharmaceutical composition comprising an ailanthone (AIL) compound or a derivative thereof, for the treatment of diseases or conditions caused by, dependent from, or associated with excessive androgen receptor activity. Ailantone compounds have been discovered to be a potent inhibitor of both full-length AR (AR-FL) and constitutively-active truncated AR splice variants (AR-Vs), and are found to possess favorable drug-like properties such as good bioavailability, high solubility, lack of CYP inhibition, and low hepatotoxicity. Methods of treatment are also provided.