Finasteride was the first 5-ARI to be introduced for medical use.  It was marketed for the treatment of BPH in 1992 and was subsequently approved for the treatment of pattern hair loss in 1997.  Epristeride was the second 5-ARI to be introduced and was marketed for the treatment of BPH in China in 2000.  Dutasteride was approved for the treatment of BPH in 2001 and was subsequently approved for pattern hair loss in South Korea in 2009 and in Japan in 2015.   The patent protection on finasteride and dutasteride has expired and both drugs are available as generic medications .  
By inhibiting 5α-reductase and thus preventing DHT production, finasteride reduces androgen signaling in tissues like the prostate gland and the scalp. In the prostate, this reduces prostate volume, which improves BPH and reduces risk of prostate cancer. Finasteride reduces prostate volume by 20 to 30% in men with benign prostatic hyperplasia.  Inhibition of 5α-reductase also reduces epididymal weight, and decreases motility and normal morphology of spermatozoa in the epididymis.  Neurosteroids like 3α-androstanediol (derived from DHT) and allopregnanolone (derived from progesterone ) activate the GABA A receptor in the brain ; because finasteride prevents the formation of neurosteroids, it functions as a neurosteroidogenesis inhibitor and may contribute to a reduction of GABA A activity. Reduction of GABA A receptor activation by these neurosteroids has been implicated in depression , anxiety , and sexual dysfunction .