Available toxicity information from clinical trials of finasteride in men with [androgenic alopecia] is very limited, is of poor quality, and seems to be systematically biased. In a cohort of men prescribed finasteride for routine treatment of AGA, most would have been excluded from the pivotal studies that supported US Food and Drug Administration approval for AGA. Published reports of clinical trials provide insufficient information to establish the safety profile for finasteride in the treatment of AGA.
—Persistent erectile dysfunction in men exposed to the 5α-reductase inhibitors, finasteride, or dutasteride: PeerJ, March 9, 2017