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 .  
Treatment of young subjects is of increasing concern due to accumulating evidence that daily use of oral finasteride has several severe adverse effects… Since finasteride inhibits T conversion into DHT, which is responsible for most androgen activity, it is plausible that prolonged finasteride use in predisposed individuals could simulate the effects of aging in young men. Since some of the effects of androgen inhibition cannot be reversed once local androgen levels are re-established, it is temping to speculate that patients could still suffer from adverse sexual effects several months or even permanently after finasteride discontinuation.
Persistent adverse effects of finasteride in younger men include erectile dysfunction, low libido, lack of orgasms, depression, and decreased alcohol consumption. One study has found lower levels of several neurosteroids in this population. Out of the various persistent side effects, erectile dysfunction and decreased alcohol consumption have been the most studied in animal models. Further research is needed on who is susceptible to the persistent adverse side effects of finasteride and on the underlying mechanisms of the medication. Irwig MS. Persistent sexual and non-sexual adverse effects of finasteride in younger men. Sex Med Rev 2014;2:24–35.