What are the unpleasant side effects of the hair growth product finasteride?

An annoying and relatively notorious side effect of the hair growth drug finasteride is that it can cause sexual side effects. But there are other unpleasant side effects as well.

Finasteride inhibits the enzyme that converts the male hormone testosterone into dihydrotestosterone (DHT). DHT plays a major role in hair loss (male pattern baldness) because it causes hair follicles on the scalp to shrink and eventually stop producing hair. By blocking this enzyme, finasteride reduces the amount of DHT in the body by approximately 60–70%, slowing hair loss and sometimes promoting new hair growth.

The main potential side effects are decreased libido (decreased sex drive), erectile dysfunction (difficulty or inability to get or maintain an erection), decreased ejaculation volume or changes in orgasm, and testicular pain. These symptoms may occur in a small percentage of users (approximately 1–2%).

In rare cases, they can persist even after stopping finasteride—this is sometimes called post-finasteride syndrome, although this topic is still under debate in the medical community.

Other, less common side effects include breast tenderness or enlargement (gynecomastia) and mood swings or feelings of depression (rare).

Source: https://academic.oup.com/jsm/article-abstract/9/11/2927/6886761

Author: Prof. Dr. Dirk Devroey - Latest update: 2025-10-31 - Copyright: Clinifacts 2026