• 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

    Simple summary: Numerous studies have shown that treatment with finasteride and dutasteride can change the size, tissue composition and function of the penis and prostate. 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); smaller cavities for blood … Read more

  • 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 or chronic abuse. This post covers post-drug disorders linked to use of alcohol, hallucinogens, antidepressants, benzodiazepenes, isotretinoin (also known … Read more

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

    Fitness influencers are followed primarily by younger men who want to be stronger, better-performing, and in some cases more attractive. This brings up the topic of hair and hair loss. In the era of Instagram, body-hacking and online prescribers such as Hims and Keeps, young men’s worries over hair loss might be greater than ever. … Read more

  • Firsthand reports – 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 the post-finasteride disorder.

  • 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. In the segment, Huberman raises an issue that has been little-discussed in the literature: the role of the androgen dihydrotestosterone (DHT) in development throughout the … Read more

  • 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 … 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.

  • 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

    In 2010, Merck requested to add a warning of depression to the Propecia label. A safety group within FDA concurred, but FDA’s dermatology products group did not support the change. Over a decade later, FDA required the addition of ‘suicidal ideation and behavior’ to the Propecia label.

  • 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.

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-AR deficiency Adverse effects Adverse event reports Animal studies Antidepressants 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 Hair transplant surgeons History Merck Merck files News Penile abnormalities Persistent adverse effects Pharmacology Pharmacovigilance Polls Post-finasteride syndrome Propecia Psychological adverse effects Recoveries 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)