Chronic treatment with finasteride daily does not affect spermatogenesis or semen production in young men.
Overstreet JW, Fuh VL, Gould J, Howards SS, Lieber MM, Hellstrom W, Shapiro S, Carroll P, Corfman RS, Petrou S, Lewis R, Toth P, Shown T, Roy J, Jarow JP, Bonilla J, Jacobsen CA, Wang DZ, Kaufman KD. Chronic treatment with finasteride daily does not affect spermatogenesis or semen production in young men. J Urol. 1999 Oct; 162(4):1295-300.