Finasteride timeline

Finasteride molecular structure from PubChem

Jump to 2021


A paper in Science reports on guevedoches, people of atypical sexual development in a remote village in the Dominican Republic. At puberty these individuals matured into males but did not show prostate growth or recession of their hairline. This work later prompted Merck to develop finasteride, branded as Proscar, to treat benign prostatic hyperplasia (BPH, or enlarged prostate). (Source: Imperato-McGinley J, Steroid 5alpha-reductase deficiency in man: an inherited form of male pseudohermaphroditism)


June: U. S. Food & Drug Administration (FDA) approves Merck’s Proscar (finasteride 5 mg/day) for treatment of benign prostatic hyperplasia (BPH).


In a internal Merck report, Dr. Martin Malkin outlines a strategy for bringing finasteride for hair loss to the market in the “most rapid registration possible.” Although Phase III clinical studies have not been completed, the report recommends describing the medication as “well-tolerated” with “mild” adverse reactions that are “not any different from patients in the placebo group.”


December: FDA approves Merck’s application for Propecia (finasteride 1 mg/day) for treatment of androgenetic alopecia (AGA, or male pattern hair loss).


The Propecia consumer label states that sexual adverse effects occurred in less than 2% of men, and “went away in men who stopped taking PROPECIA. They also disappeared in most men who continued taking PROPECIA.”

FDA approves GSK’s Avodart (dutasteride, also a 5-alpha reductase inhibitor) for treatment of benign prostatic hyperplasia (enlarged prostate). (Drug label)


The Yahoo support group Finasteride Side Effects is founded (Source: PropeciaHelp: About)


PropeciaHelp support site launched. (Source: PropeciaHelp: About)

November: In response to online reports of persistent sexual adverse effects of finasteride, the Swedish Medical Products Agency requests Merck to provide a complete listing of the outcome “in terms of reversibility” of all adverse event cases related to the male reproductive system. In a Periodic Safety Update Report, Merck reports the following:

  1. In Phase III clinical trials conducted in the 1990s, one man who discontinued the trial reported that a sexual AE related to taking Propecia was unresolved six months after discontinuing the drug.
  2. 16 men who had a drug-related sexual AE and stayed in the trial, did not have resolution of the AE during the trial.
  3. Among cases of sexual AEs from Propecia reported to Merck, 200 men had the outcome “Not recovered,” while 215 men had the outcome “Unknown.”


Merck added the following language to the ‘Undesirable Effects’ section of the Propecia product monograph in Sweden: “In addition, the following have been reported in post-marketing use: persistence of erectile dysfunction after discontinuation of treatment with PROPECIA.” (Source: Miller v. Merck Frosst Canada Ltd., 2013)


February: Merck releases an internal Risk Management Plan identifying the following as ‘Important Potential Risks’: Persistence of Erectile Dysfunction, Male Infertility and Depressive Disorders. (Source: Risk Management Plan, p. 55)


February: Two men file a lawsuit against Merck in the U.S. District Court of New Jersey, alleging negligence and failure to warn about serious sexual dysfunction from taking Propecia (Case 3:11-cv-00641).

March: Depression is added as an adverse event in the Postmarketing Experience section of the drug label.

November: The product monograph for Propecia in Canada is updated to warn that sexual dysfunction could persist after discontinuation of treatment. (Source: Miller v. Merck Frosst Canada Ltd., 2013)

The first medical articles appear on persistent sexual adverse effects of finasteride, by Abdulmaged Traish et al. and Michael Irwig & Swapna Kolukula.


April: FDA releases a revision to the Propecia label. Added to the Postmarketing Experience section are sexual adverse effects which continued after stopping the drug.

The Post-Finasteride Syndrome Foundation (PFS Foundation) is founded in New Jersey by John Santmann.

Michael Irwig publishes article on depressive symptoms and suicidal thoughts among former users of finasteride.


January: Merck patent on Propecia expires. (Sources: Consumer Reports and Merck 10-K filing)


Kelly Pfaff files a lawsuit against Merck concerning her husband’s health problems and death by suicide after using finasteride. (Source: Reuters)


PFS Foundation files Citizen Petition with FDA to remove finasteride for hair loss from the market or add a black box warning.

Telepharmacy Hims is founded. The company sells finasteride for hair loss using online marketing and telemedicine consultations with doctors.


Most of the ~1,100 plaintiffs who sued Merck over adverse effects of Propecia accept a settlement offer from the company. (Sources: Reuters | Motion and Memorandum for Approval of Settlement Plan)

Telepharmacy Keeps, selling finasteride and other hair loss treatments, accepts $15 million in financing from two venture capital firms. (Source: TechCrunch)


June: A study reports penile vascular abnormalities in 68% of young men with persistent adverse effects after using finasteride or dutasteride as a treatment for hair loss.

November: A study of suicidality and psychological adverse events of finasteride is published in leading dermatology journal JAMA Dermatology.

December: PFS Foundation files supplements to 2017 Citizen Petition to FDA to remove finasteride from market or add a black box warning.


January: Telepharmacy Hims becomes a public company in a SPAC transaction. (Source: TechCrunch)

U.S. Magistrate Judge Peggy Kuo orders Propecia litigation documents to be unsealed. (Source: Reuters)

February: PropeciaHelp launches, a community to raise awareness and understanding of ‘post-finasteride syndrome’.

June: Merck announces completion of the spinoff of a new company, Organon, with Propecia included in Organon’s product portfolio.

June: FDA adds a new adverse event, hematospermia (blood in semen), to the Postmarketing Experience section of the Propecia label. (Sources: Drugs@FDA: Label | Letter)

July: A study reporting altered gene expression in PFS patients is published in the Journal of Sexual Medicine: Howell S, et al. Differential Gene Expression in Post-Finasteride Syndrome Patients.

September: Public Citizen files a lawsuit against FDA for inaction on Propecia (Sources: Reuters | Public Citizen). Case is assigned to Chief Judge Beryl A. Howell of the U.S. District Court of the District of Columbia.

October: In the lawsuit Post-Finasteride Syndrome Foundation v. FDA, Judge Howell grants FDA’s motion to stay proceedings until June 15, 2022. A joint status report by the two parties is due by June 13, 2022.

See also a brief history of research on finasteride.