5-alpha reductase is the enzyme that converts testosterone to DHT; some medicines block it.
5-alpha reductase inhibitors reduce conversion of testosterone to DHT. Finasteride mainly targets type II 5-alpha reductase, while dutasteride inhibits both type I and type II. These medicines are among the most effective pharmacological options for male pattern hair loss, but they need careful counselling because sexual and mood-related side effects can occur. The term “DHT blocker” is often used online for supplements as well as medicines, but this can be misleading. Prescription medicines have stronger evidence; many supplement claims are weaker or unproven.
Anastassakis K. Androgenetic Alopecia From A to Z, Vol. 2, Springer, 2022 — https://doi.org/10.1007/978-3-031-08057-9; British Association of Dermatologists: Hair loss male pattern (androgenetic alopecia) — https://www.bad.org.uk/pils/hair-loss-male-pattern-androgenetic-alopecia; MHRA Drug Safety Update: Finasteride and Dutasteride updated safety warnings, 11 May 2026 — https://www.gov.uk/drug-safety-update/finasteride-and-dutasteride-updated-safety-warnings-for-psychiatric-side-effects-and-sexual-dysfunction
