Finasteride (Propecia) is an Androgen Inhibitor medication. It is commonly used for the treatment of male pattern baldness and enlarged prostate. Finasteride is not routinely used in the treatment of acne.

Finasteride inhibits the synthesis of the powerful androgen (male hormone), DHT. DHT is closely related to Testosterone, but is more potent. Inhibiting the effects of androgen hormones can help improve acne symptoms in some individuals by slowing the growth of the sebaceous glands. In individuals with androgen-induced acne, high levels of androgen hormones cause increased sebaceous gland activity, which leads to elevated sebum production, clogged pores and excessive growth of acne-causing P. acnes bacteria inside follicles.

Finasteride works by blocking the activity of an enzyme called 5-aplha reductase, which converts testosterone into dihydrotestosterone (DHT). There are two different versions of the 5-alpha reductase enzyme in humans. Dutasteride is an Androgen Inhibitor that is closely related to Finasteride. Dutasteride is a more powerful inhibitor of DHT synthesis than Finasteride because it inhibits both forms of the enzyme, while Finasteride only inhibits one.

Androgen hormones are an essential part of male biology. Because Androgen Inhibitors have significant side effects when used in men, they are usually only used to treat acne in women. However, Finasteride is one of the few Androgen Inhibitors that is routinely used in men. Two of the most common side effects of Androgen Inhbitor use in men are a reduced sex drive and decreased muscle mass.

Finasteride is generally available in oral formulations, but topical Finasteride may be better suited for use as an acne treatment. Finasteride is readily absorbed into the skin, and topically applied Finasteride is expected to have substantially fewer side effects than oral Finasteride. Topical Finasteride solutions are available, although many of them also contain the hair growth stimulator Minoxidil (Rogaine).