Finasteride (Propecia®)

Finasteride in Brief
  • Generic name : Finasteride
  • Brand names: Propecia® , Proscar®
  • Therapeutic class: Hair regrowth stimulant
  • Pharmacologic class: Type II 5-alpha reductase inhibitor
  • FDA Approved: December 22, 1997
  • Pregnancy Category: X (contraindicated in pregnant women)
  • Originally discovered: 1990s, Merck & Co, USA USA

by eMedExpert staff
Medical references reviewed: August, 2018


Propecia is a specific type II 5-alpha reductase inhibitor. It inhibits the enzyme responsible for regulating conversion of testosterone to dihydrotestosterone (DHT). By reducing DHT levels in the scalp, finasteride decreases DHT's effects on the hair follicles, reversing the process of hair loss.

Finasteride significantly reduces hair loss progression and restores hair growth in men with male pattern hair loss.



Finasteride was originally developed by Merck to treat BPH (benign prostatic hyperplasia) or an enlarged prostate. It was subsequently discovered that people who were taking Proscar were experiencing hair regrowth.

Merck & Co started clinical testing in the early 90s to evaluate the effectiveness of finasteride in treating hair loss. To minimize the potential of side effects that come with Proscar (5 mg finasteride), Merck & Co. conducted clinical testing on 1 mg finasteride as a treatment for hair loss.

On December 22, 1997 the FDA approved Propecia (finasteride 1 mg) for the treatment of androgenic alopecia in men.

FDA approved uses

  • Treatment of male pattern hair loss (androgenic alopecia) in men only.
  • Treatment of symptomatic benign prostatic hyperplasia (BPH) in men with enlarged prostate; in combination with doxazosin to reduce the risk of symptomatic progression of BPH.

Off-label & Investigational uses

  • Hirsutism in women1
  • Hair transplant4
    Finasteride improves scalp hair and growth of nontransplanted hair in areas surrounding the transplant.
  • Androgenetic alopecia in women 9 (role of finasteride for pattern hair loss in women is still controversial)
  • Hidradenitis suppurativa (acne inversa)11, a chronic, recurrent, inflammatory skin disease

Finasteride "pros" and "cons"

Because male pattern hair loss is essentially a cosmetic problem, it is important to be fully informed of both the "pros" and "cons" of finasteride before treatment decisions are made.


  • Effective: increases hair growth and prevents further hair loss. The vast majority of men using finasteride experience some benefit from its use2. Men with mild to moderate, but not complete, hair loss can expect a favorable outcome.
    The success rate of Propecia in the improvement of hair growth varies from 58 to 66%6-8.
    The success rate in the prevention of further hair loss is up to 83%7.
  • Lack of drug interactions. Finasteride has not been shown to interfere with other medicines.
  • Suitable for long-term treatment. Follow-up studies have reported that it is safe and effective over the long-term5. No major side effects have been seen with finasteride 1 mg for up to 5 years.
  • Good tolerability.


  • Not a cure for hair loss. Unfortunately, Propecia does not 'cure' male pattern hair loss. Any benefits are lost when the medication is stopped. It will only work over the long term if you continue taking it. If you stop, you will likely lose any hair you have gained within 12 months of stopping treatment.
  • Not suitable for women. Finasteride has not been proven to be effective in postmenopausal women3. Because of the risk of finasteride causing malformation in male fetuses, clinical tests in women androgenetic alopecia were originally restricted to post menopausal women.
  • Sexual side effects, such as difficulty in achieving an erection, less desire for sex, decreased amount of semen released during sex (this decrease does not appear to interfere with normal sexual function). These side effects are usually reversible after discontinuation of finasteride, but may persistent10.
    Sexual side effects are most prominent during the first year.
  • Some men may develop gynecomastia (breast enlargement).
  • High cost.


Mode of action

Finasteride is the 5alpha-reductase inhibitor. The 5alpha-reductase is an enzyme that catalyzes the conversion of testosterone to dihydrostestosterone (DHT), progesterone to dihydroprogesterone and deoxycorticosterone to dihydrodeoxycorticosterone.

Male pattern hair loss, or androgenetic alopecia, is an androgen-dependent disorder. In genetically susceptible men, dihydrotestosterone, a potent metabolite of the male androgen testosterone, contributes to male pattern hair loss.

The conversion of testosterone to DHT is regulated by the enzyme 5-alpha reductase. Finasteride inhibits this enzyme, thereby reducing DHT levels in the scalp and DHT's harmful effects on the hair follicles, reversing the process of hair loss.

Finasteride decreases DHT concentrations in the serum and the scalp by up to 70 and 60%, respectively.

Finasteride does not stimulate hair growth on other parts of the body.

How long does it take for Propecia for hair regrow?

Male pattern hair loss is a condition that develops over a long period of time. Because it takes time for new hair to grow, you will not see immediate results. In general, daily use for 3 months or more may be necessary before you notice increased hair growth or prevention of further loss.

If you stop taking Finasteride, DHT levels will rise again in the scalp, and your hair loss is likely to resume.

Time to clear out the system

Finasteride half-life is 6 hours (range 3-16).

Further reading


  • 1. Lakryc EM1, Motta EL, Soares JM Jr, Haidar MA, de Lima GR, Baracat EC. The benefits of finasteride for hirsute women with polycystic ovary syndrome or idiopathic hirsutism. Gynecol Endocrinol. 2003 Feb;17(1):57-63. PubMed
  • 2. Kaufman KD, Olsen EA, Whiting D, Savin R, DeVillez R, Bergfeld W, Van Neste D, Roberts JL, Hordinsky M, Shapiro J, Binkowitz B, Gormley GJ. Finasteride in the treatment of men with androgenetic alopecia. J Am Acad Dermatol. 1998 Oct;39(4 Pt 1):578-89. PubMed
  • 3.Roberts JL, Hordinsky M, Olsen EA, Savin R, Bergfeld W, Fiedler V, Lucky A, Whiting DA, Pappas F, Culbertson J, Kotey P, Meehan A, Waldstreicher J. Lack of efficacy of finasteride in postmenopausal women with androgenetic alopecia. J Am Acad Dermatol. 2000 Nov;43(5 Pt 1):768-76. PubMed
  • 4. Leavitt M, Perez-Meza D, Rao NA, Barusco M, Kaufman KD, Ziering C. Effects of finasteride (1 mg) on hair transplant. Dermatol Surg. 2005 Oct;31(10):1268-76.
  • 5. Menefee E, Sanchez M, Kaufman KD. Changes in hair weight in men with androgenetic alopecia after treatment with finasteride (1 mg daily): three- and 4-year results. J Am Acad Dermatol. 2006 Jul;55(1):71-4.
  • 6. Kawashima M, Hayashi N, Igarashi A, Kitahara H, Maeguchi M, Mizuno A, Murata Y, Nogita T, Toda K, Tsuboi R, Ueki R, Yamada M, Yamazaki M, Matsuda T, Natsumeda Y, Takahashi K, Harada S. Finasteride in the treatment of Japanese men with male pattern hair loss. Eur J Dermatol. 2004 Jul-Aug;14(4):247-54. PubMed
  • 7. McClellan KJ, Markham A. Finasteride: a review of its use in male pattern hair loss. Drugs. 1999 Jan;57(1):111-26. PubMed
  • 8. Lin JH, Chen WC. Finasteride in the treatment of Taiwanese men with androgenetic alopecia: a 12-month open-label study. Kaohsiung J Med Sci. 2002 Aug;18(8):379-85. PubMed
  • 9. Boersma IH, Oranje AP, Grimalt R, Iorizzo M, Piraccini BM, Verdonschot EH. The effectiveness of finasteride and dutasteride used for 3 years in women with androgenetic alopecia. Indian J Dermatol Venereol Leprol. 2014 Nov-Dec;80(6):521-5. PubMed
  • 10. Guo M, Heran B, Flannigan R, Kezouh A, Etminan M. Persistent Sexual Dysfunction with Finasteride 1 mg Taken for Hair Loss. Pharmacotherapy. 2016 Nov;36(11):1180-1184 PubMed
  • 11. Khandalavala BN, Do MV. Finasteride in Hidradenitis Suppurativa. J Clin Aesthet Dermatol. 2016 Jun;9(6):44-50 PubMed

Published: November 03, 2008
Last updated: July 30, 2018

Interesting facts
Propecia Merck
  • Propecia remains the first and only FDA-approved oral medication for hair loss.
  • At the end of 2004 the World Anti-Doping Agency added finasteride to its list of banned agents in international sports. The agency calls finasteride a masking agent that hides the use of more nefarious drugs like the steroid nandrolone.
  • Finasteride 2.5 mg daily combined with an oral contraceptive containing drospirenone and ethinyl estradiol (e.g. Yasmin, Yaz) may improve Female Pattern Hair Loss at 1 year.

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