• A proposed explanation of lasting dysfunctions after use of finasteride or dutasteride

    Men who previously took finasteride and dutasteride have reported sexual dysfunction, anxiety, depression, cognitive problems and other dysfunctions which have continued long after stopping the drug. This paper proposes an explanation for how these dysfunctions may develop.


  • Musculoskeletal adverse events of finasteride

    When men take finasteride for hair loss, their attention is directed to the hair and scalp. When adverse events (AEs) occur in other systems and areas of the body, it might not be obvious that finasteride could be the culprit. But Merck’s research established that the drug serves to lower dihydrotestosterone in the blood as … Read more


  • Disability and deaths in men who used finasteride

    Databases of drug adverse events contain tremendous variation. They include reports from patients of all ages, and many took other drugs that might explain outcomes. In this analysis, cases were limited to men ages 18–40 where the ‘Suspected Product’ field only contained finasteride or minoxidil. This is only a fraction of total cases, but helps … Read more


  • From the deep: why finasteride harms took decades to emerge

    Researchers blamed growing safety concerns on patients, overlooking social context and weaknesses in safety regime The official view of Propecia, fashioned by Merck at a reported cost of $450 million, is that the drug is safe and effective. Upon approval by FDA in 1997, this view was carried forward by dermatologists, some of whom were … Read more


  • FDA quashed internal warning on suicidality linked to Propecia; changed course in 2022

    KEY POINTS In 2010, Merck requested to add ‘depression’ to adverse events in the Propecia label. A safety group within FDA concurred, and also recommended adding ‘suicidal thoughts and behavior.’ FDA’s dermatology products group did not support adding a suicidality warning. Only ‘depression’ was added to the label in 2011. Over a decade later, in … Read more


  • Meta-analysis launders safety data from old pharma trials; blames patients for drug harms

    26 of 28 included studies were sponsored by Merck or GSK, representing 99.6% of the weighted data. Authors use on-drug trial data as a proxy for a post-drug syndrome—a fatal flaw.


  • Context matters: a rebuttal to yet another analysis of adverse events of finasteride

    This post responds to a recent research letter: Disproportional signal of sexual dysfunction reports associated with finasteride use in young men with androgenetic alopecia: a pharmacovigilance analysis of VigiBase.


  • A tweeted rebuttal to yet another analysis of finasteride adverse events: Nguyen et al, 2022

    A thread originally posted on Twitter is reproduced below. For an in-depth version, see the essay Context matters. See also a critique of three previous papers with similar designs, findings and conclusions. Twitter thread Nguyen et al, 2022 is the fourth analysis of adverse events of finasteride to appear since 2018. All four studies play … Read more


  • How was finasteride invented?

    Although finasteride came on the market in the 1990s, the science that led to its development began two decades earlier. The rationale for the drug emerged from a study of a unique group of people in a remote village in the Dominican Republic called Las Salinas. Locals there have long known about children who follow … Read more


  • Merck’s Propecia business

    HIGHLIGHTS Estimated Propecia revenue from 1999–2015: $5.2 billion Rough estimate of operating profit from Propecia: $4.2 billion Merck received FDA approval for Propecia (finasteride 1 mg/day) in December 1997. Sales in the first year of marketing were reported to be $76 million. The peak years were 2010–2011, when Merck reported $447 million in Propecia sales … Read more


  • Since 1994, Merck has been aware of unresolved sexual dysfunction in men who stopped taking finasteride

    Six months after discontinuing a Phase 3 finasteride trial, a man’s sexual adverse experience was unresolved. There were also 16 men whose drug-related sexual adverse experiences were unresolved at the conclusion of the trial.


  • The Merck files, part 3: Propecia lawsuits

    Filings from lawsuits alleging persistent adverse effects of Propecia and Proscar in various jurisdictions in the United States and Canada, dating from 2011 to 2021.


  • The Merck files, part 2: Merck responds to regulatory concerns about persistent adverse effects of Propecia

    These documents from 2006–2009 concern Merck’s response to postmarketing reports of persistent erectile dysfunction, male infertility and depressive disorders, among other adverse events, associated with use of finasteride. In 2006, the Swedish Medical Products Agency asked Merck for an analysis of all adverse events affecting the male reproductive system which persisted after stopping Propecia. In … Read more


  • The Merck files, part 1: An inside look at the development of Propecia

    Merck first developed finasteride for benign prostatic hyperplasia, a condition typically found in men aged 55 and older. After receiving approval for the application in 1992 and bringing the drug to market as Proscar, Merck decided to seek approval of finasteride for male pattern hair loss—to be branded as Propecia. In a 1994 memo below, … Read more


  • The Merck files: a series

    Selected documents from Propecia litigation were released by court order in 2021. This series walks through these documents, revealing Merck’s strategy for discounting safety concerns arising from clinical trials and adverse event reports. The collection is divided into three parts: 1. An inside look at the development of Propecia (1994–2001) 2. Merck responds to regulatory … Read more


  • When medical treatment brings on disease: iatrogenic disorders

    Those who have lasting dysfunctions after taking finasteride or dutasteride are not the only ones whose lives have been altered for the worse because of a medical treatment. This post summarizes diseases and conditions that may arise from medical treatments: five in dermatology, four in psychiatry and one in general medicine. ↓ Jump to the … Read more


  • Merck communications regarding reports of persistent erectile dysfunction and depression associated with finasteride

    See also: The Merck files: a series In regulatory, internal and media communications in the 2000s, Merck responded to concerns about reports of adverse events associated with Propecia, including persistent erectile dysfunction and depression. These documents seek to discount the validity of these reports by way of the following points: “insufficient” information including lack of … Read more


  • Tapped by Merck for litigation defense, a clinician-researcher sowed doubts about finasteride harms

    A 2018 article disclosed that Dr. Kevin McVary had been retained as an expert for Merck’s defense in litigation regarding persistent adverse effects (AEs) of finasteride.1 Dr. McVary has also been relatively active as a contributor of three conference abstracts, an original article, an expert review, a quote in a media story and a symposium presentation … Read more


  • Responding to a literature of doubt: limitations of three studies of adverse events of finasteride and dutasteride

    A fourth study has been published in the ‘literature of doubt’. Read the rebuttal. Background on the co-author of Baas et al, 2018 with a disclosed conflict of interest is here. Three studies analyzing adverse event (AE) data related to finasteride and dutasteride were published from 2018–2020 (the “AE papers”).1–3 The first to appear, by Baas … Read more


  • Research review: Alterations to penile and prostatic tissue associated with finasteride and dutasteride treatment

    Simple summary: Numerous studies have shown that treatment with finasteride and dutasteride can change the size, tissue composition and function of the prostate and penis. Changes in the penis linked to finasteride or dutasteride treatment include: reduced size and weight; reduced erectile response; decreased smooth muscle; increased collagen density; fibrosis (scarring or other tissue abnormalities); … Read more


This site describes adverse experiences which some may find disturbing. See the Reader advisory.

Places to start

  • Thinking about taking finasteride for hair loss? See Weighing the risks.
  • This post compiles research on changes in penile tissue and function associated with finasteride and dutasteride treatment.
  • For a historical perspective, see the timeline which starts with a study in Dominican Republic in the early 1970s.
  • The research bibliography gathers hundreds of papers on adverse effects of finasteride and other 5-alpha reductase inhibitors. See also Research by system & function.

Tags

5-AR deficiency Adverse effects Adverse event reports Animal studies Anxiety Business Clinical trials Commentary Conflict of interest Deaths Denial and skepticism Depression Dermatologists Dermatology Disability Doctor views Documents Drug label Dutasteride Etiopathology Europe FDA Firsthand reports FOIA requests Hair transplant surgeons History Litigation Merck Merck files Meta-analysis Musculoskeletal Persistent adverse effects Pharmacovigilance Post-finasteride syndrome Propecia Psychological adverse effects Recoveries Research Researchers Revenue Sexual adverse effects Sexual dysfunction SSRIs Urology Vigibase

Harvesters by Pieter Breughel the Elder, 1565 (via Met Museum Open Access)