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.
—Immunohistochemical Evaluation of Androgen Receptor and Nerve Structure Density in Human Prepuce from Patients with Persistent Sexual Side Effects after Finasteride Use for Androgenetic Alopecia: PLOS ONE, June 24, 2014