Brand Name Manufacturers

Proscar by Merck
Propecia by Merck

Generic Manufacturers



Androgen conversion inhibitor. Inhibits the production of dihydrotestosterone (DHT) from testosterone by inhibiting the binding of 5a-reductase, which is the enzyme responsible for converting testosterone to DHT. DHT is the active androgen found in the skin and prostate gland, and is associated with the development of male pattern baldness, excess body hair, and benign prostatic hypertrophy. Not suitable as a general anti-androgen since it only affects DHT production. However, it seems to be more helpful in counteracting male-pattern baldness and excess body hair than general anti-androgens.


5mg oral tablets (Proscar)
1mg oral tablets (Propecia)

Typical dosage

Pre-op 0.05-1mg/day
Post-op 0.05-1mg/day
(See comments below)


Approved by U.S. FDA


Benign prostate enlargement


Hypersensitivity to any component of the product.

Adverse reactions

Generally mild and transient


Anecdotal evidence strongly suggests that pill fragments (say, 4-12 from each pill) taken daily are just as effective as taking the entire pill. There might issues with oxidation, so avoid handling the unused fragments, and keep them in a small, air-tight container.

Pre-ops who take finasteride should consider coadministration of a more general anti-androgen such as spironolactone (since finasteride only blocks conversion of testosterone to DHT, the body sometimes boosts the testosterone level in response.)

On the subject of scalp hair regrowth: In addition to finasteride therapy, it is customary to apply minoxidil 5% (topical) daily to the balding scalp area in order to achieve maximum results. Some people also add tretionin (retinois acid) creme 0.05%, but it is not yet clear whether that always helps (and speaking of minoxidil: note that a few people have reported that it seemed to have a systemic effect, in that it increased body hair even though it was applied only to the scalp).

Do not let a female who is pregnant, or might be pregnant, anywhere near finasteride fragments or powder. It is a strong teratogen, known to cause intersexed genital expression in the male fetus.

Based on rabbit and rat studies, there may be a slight effect on male fertility that would reverse within 6 weeks of discontinuing.