Antiandrogens are a group of drugs that block the action of androgens by two broad mechanisms: competitive inhibition of binding of androgens (testosterone and dihydrotestosterone [DHT]) to the androgen receptor and inhibition of the enzyme 5α-reductase that converts testosterone to DHT. Androgen receptor antagonists include drugs, such as the steroidal antiandrogens, spironolactone and cyproterone acetate, which also have direct inhibitory effects on androgen synthesis, and the non-steroidal or ‘pure’ antiandrogens, which are flutamide, bicalutamide, enzalutamide, darolutamide and apalutamide. Flutamide is a potent antiandrogen. Finasteride has a much shorter half-life than dutasteride. Antiandrogens are contraindicated during pregnancy due to the risk of feminization of the male fetus. Small amounts of finasteride/dutasteride have been detected in the semen of males taking this medication. It is not known whether a male fetus may be adversely affected by in utero exposure to the semen of a male treated with finasteride or dutasteride, but condom use is advised.