Originally developed to treat benign prostatic hyperplasia (BPH), finasteride was found to have hair growth effects, leading Merck to launch Propecia™ in 1997 as the first FDA-approved 5-alpha reductase inhibitor for male pattern baldness. Despite known side effects like sexual dysfunction, dermatologists often failed to inform patients adequately about these risks before prescribing the drug. Consequently, many young men who took finasteride experienced side effects such as reduced sexual function, and some reported persistent symptoms even after discontinuing the drug, known as “Post-Finasteride Syndrome (PFS).”

Finasteride is taken at 1 mg per day for hair loss treatment, significantly lower than the 5 mg dosage for BPH treatment, yet PFS is more commonly reported among hair loss patients. There are three primary reasons for this: (1) older BPH patients tend to prioritize urinary relief over potential sexual side effects, (2) urologists prescribing Proscar™ are generally more aware of sexual side effects and obtain thorough consent, and (3) urologists are more likely to provide erectile dysfunction medications (e.g., Viagra®) to manage sexual side effects.

PFS symptoms include various sexual dysfunctions (e.g., penile atrophy, tissue changes, decreased ejaculate volume and quality, reduced libido, erectile dysfunction, decreased penile sensation, and reduced orgasm) as well as neurological and psychological symptoms like depression, anxiety, panic attacks, insomnia, anhedonia, poor concentration, memory impairment, and suicidal ideation. While finasteride appears to be a trigger, the exact cause of PFS remains unclear, and the persistence of symptoms after discontinuation is not fully understood.

The existence of PFS remains controversial. A 2019 BMJ editorial described PFS as an “ill-defined and controversial” condition. Some argue it resembles other self-diagnosed “mystery syndromes” like Morgellons or multiple chemical sensitivity, while some biomedical researchers consider it a real and serious condition based on existing evidence. Additionally, various studies have found associations between finasteride use (and cessation) with depression, suicidal ideation, and sexual dysfunction, but the quality of evidence is limited. As a result, the medical community is divided on the existence of PFS, and the lack of clear diagnostic criteria and underlying biological mechanisms makes it difficult to assess the condition.

While the number of people using finasteride in various forms has increased, PFS remains rare. However, for a small number of men, PFS can be a severe and persistent issue. Some patients, physicians, and attorneys have filed lawsuits claiming that PFS is a long-term effect of taking finasteride.

Most lawsuits against Merck, the manufacturer of finasteride, have been dismissed due to lack of evidence, and multidistrict litigation has concluded without finding any liability. However, these lawsuits prompted the FDA to require Merck to add warnings about potential side effects and post-cessation syndrome to Proscar™ and Propecia™ labels. In 2017, the Post-Finasteride Syndrome Foundation petitioned the FDA to ban finasteride or strengthen warnings, citing scientific studies. Still, in 2022, the FDA rejected the petition due to a lack of conclusive evidence directly linking PFS symptoms to the drug. However, based on patient reports, the FDA asked Merck to add “suicidal thoughts and behavior” as a potential side effect on the Propecia™ label. In South Korea, similar warnings were added to finasteride-based hair loss and BPH medications by the Ministry of Food and Drug Safety as early as July 2017.

PFS remains a contentious topic, requiring further research and clear diagnostic criteria. Although the number of men reporting persistent side effects is rising, no evidence-based treatment for PFS currently exists. Until more research and definitive diagnostic criteria are established, the debate surrounding PFS is likely to continue.