• How Merck buried finasteride’s full impact on hormone signaling

    Merck held that finasteride had a simple and selective mechanism. In fact, it disrupts hormonal pathways much more broadly. These pathways support the brain, reproductive system and other organs. Merck’s selective account concealed risks which would surface in the decades after approval of Propecia.

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

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

  • Response to Dr. Ralph Trüeb’s writings on post-finasteride syndrome

    A drug-induced syndrome is all in the mind, a Swiss doctor wrote. Editors at the journals had past ties to the drug maker. Men turn to finasteride to try to save their hair, but they might end up with a severe and lasting disability.1 There are countless stories online, usually anonymous because of the embarrassing…

  • Appendix: response to Trüeb

    This appendix accompanies the article: Response to Dr. Ralph Trüeb’s writings on post-finasteride syndrome. Table of competing interests ↑ back to text Engagements with Merck re: Propecia Skin Appendage Disorders (journal) (1) International Journal of Trichology (2) Experimental Dermatology (journal) Hair Growth and Disorders textbook (2008) Cited by Trüeb Ralph Trüeb, MD Member, Editorial Board…

  • Seeking a medical sign of genital numbness

    Some post-5ARI patients experience genital numbness. This symptom can be assessed, but the tests are not easily accessible. This post gives an overview of medical tests which could yield signs of genital numbness and other abnormalities.

  • Mid-year update

    Drug regulators in France and Canada announced new warnings. A popular podcast discussed post-finasteride syndrome, while men’s fitness influencers urged followers to avoid finasteride.

  • The lost men: how Merck, GSK papered over bad outcomes in trials

    A re-examination of clinical trials of finasteride and dutasteride reveals warning signs of long-term harms to surface later.

  • The lost men – appendix

    A summary of men who had unresolved and severe adverse events in clinical trials of finasteride and dutasteride.

  • From LSD to Zoloft, drugs can leave lasting damage

    SUMMARY: Post-drug disorders are not side effects that linger, but lasting changes that may be severe and irreversible. These disorders are linked to prescribed drugs as well as recreational drugs, and can arise after one dose, long-term use, or abuse. This post covers post-drug disorders linked to use of alcohol, hallucinogens, antidepressants, benzodiazepenes, isotretinoin (also…

  • Men’s fitness influencers are raising alarms about finasteride risks

    Fitness influencers draw in an audience of younger men who want to be stronger, better-performing, and in some cases more attractive. Some guys worry that hair loss will dim their prospects for dating, sex and relationships—or even professional success. In the era of Instagram, body-hacking and telehealth companies such as Hims and Keeps, young men’s…

  • Firsthand experiences – Volume XIII: User reviews

    The websites Drugs.com and Ask a Patient collect reviews of drugs. Here are selected reviews of finasteride, taken by men for hair loss conditions. The dates range from 2008 to 2023.

  • Firsthand experiences – Volume XII: Dutasteride

    Along with finasteride and saw palmetto, dutasteride has been linked a post-drug disorder in some men. This post contains firsthand reports of lasting dysfunctions after taking dutasteride, and stopping the drug.

  • Firsthand experiences – Volume XI: Videos

    Click the video title to view on YouTube where you’ll find a description and comments.

  • Firsthand experiences – Volume X: Saw palmetto & nettle

    Men turn to saw palmetto, a plant-based supplement, because prescription drugs may be unavailable or too costly. Some see the palm supplement as having a lower risk of side effects. Regulators say it is safe, but online, it is not difficult to find reports of men with adverse experiences after using saw palmetto which resemble…

  • Andrew Huberman, PhD discusses post-finasteride syndrome on the Huberman Lab podcast

    Today’s episode of the popular Huberman Lab Podcast is titled “The Science of Healthy Hair, Hair Loss and How to Regrow Hair.” It includes a five-minute discussion of post-finasteride syndrome. Huberman raises an issue that has been little-discussed in the literature: the role of the androgen dihydrotestosterone (DHT) in development throughout the lifespan. While we…

  • Regulators are waking from their slumber

    Agencies in France, the United Kingdom, Canada and the United States are strengthening warnings about finasteride risks

  • Elements of a drug safety disaster

    Over the past 25 years, finasteride harms have spread invisibly, altering lives and giving rise to confusion and disagreement. This post identifies common themes across all these spheres. Many of these have to do with biases, omissions and collusion among industry, physicians and regulators.

  • 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…

  • 2022 – year in review

    Regulators added warnings, the New York Post covered finasteride harms, and two influencers urged followers to avoid the drug.

  • 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…

  • 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…

  • 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 alters levels of chemical messengers in the blood as well as peripheral…

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.


5-alpha syndrome 5-AR deficiency Adverse effects Adverse event reports Animal studies Anxiety Bias Bibliography Clinical trials Conflict of interest Denial and skepticism Dermatologists Dermatology Doctor views Documents Drug label Dutasteride Europe FDA Firsthand reports Fluoroquinolones FOIA requests History Merck Merck files News Penile abnormalities Persistent adverse effects Pharmacology Pharmacovigilance Polls Post-finasteride syndrome Propecia Psychological adverse effects Recoveries Regulation Research Sexual adverse effects Sexual dysfunction Shame and stigma Social attitudes Social context Social media SSRIs Video

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