• A rundown of new bibliographies & research guides

    The research base spans many disciplines and goes back almost 50 years. To help researchers get oriented, an on-ramp was added. In the Systems & functions area, a new bibliography was added: Adverse effects on skin, comprising nine case reports. The gynecomastia bibliography has been expanded. The bibliography on the musculoskeletal system has been expanded … Read more


  • 2022 – year in review

    Regulators added warnings, the New York Post covered finasteride harms, and two influencers urged followers to avoid the drug 1. In the long war over finasteride safety, social taboos around sexuality and mental state have played an important, but overlooked role. Read about their role in this post: From the depths: why finasteride harms took … Read more


  • Rules of engagement: how sensitive concerns are hidden from drug trials

    Alan, a 28-year-old man who experiencing hair loss, is participating in the Propecia clinical trial. Alan brings high hopes that the new drug will stop hair loss. An investigator examines Alan’s scalp and hair, recording figures on a form. She asks Alan if he experienced any side effects. None, he replies. He is then given a form to fill out…


  • Polls vs. official data on side effect rates

    Since online polls are anonymous, there is less risk to disclosing embarrassing side effects. In online polls, the rate of side effects was 6.2x greater than the rate of adverse events in a clinical trial. The clinical setting may suppress safety concerns in sensitive areas such as sexuality and mental state.


  • Appendix: Results of online polls on side effects

    This is an Appendix to the post: Polls vs. official data on side effect rates. Summary Mobile users: swipe left to see more columns. ID & source Date posted Participants % with side effects % with severe or persistent side effects P1. r/tressless Jan 2016 146 53.4% NA P2. r/HairLoss Jul 2021 110 27.3% NA … Read more


  • Recent developments

    In June 2022, the FDA required the addition of ‘suicidal ideation and behavior’ to the Propecia (finasteride 1 mg) label. In July, France’s national drug regulator ANSM added materials to help patients better understand the risks of finasteride.


  • Hair or manhood—choose one?

    In ancient Greece, Hippocrates and Aristotle observed that eunuchs did not go bald. Jumping ahead to the early 1940s, American anatomist James B. Hamilton reviewed histories of men with testosterone deficiency and found a pattern: the earlier the age of hormone deficiency, the less balding occurred.


  • 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 the drug serves to lower dihydrotestosterone in the blood as well as peripheral tissue … 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, in the comparison below, minoxidil). This is only a fraction of … Read more


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

    Physician-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

    Despite serious methodological shortcomings—including the preposterous use of on-drug safety data as a proxy for a post-drug condition—the authors nevertheless blame the post-drug syndrome on patient shortcomings. Zhang et al. have yoked bad logic to biased data in order to deflect attention away from drug harms.


  • 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

    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 underlying research 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 an unusual developmental path: … Read more


  • Merck’s Propecia business

    HIGHLIGHTS 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 in each year. In total, Merck booked an estimated $5.2 billion in sales of Propecia. We … 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 physician-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


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

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