Q: Does finasteride need to be taken every day? — M.B., Atlanta, GA

A: Finasteride (Propecia) is a competitive inhibitor of Type II, 5 alpha-reductase (5AR is the enzyme that converts Testosterone to DHT which then causes hair to miniaturize and eventually be lost). Finasteride is 100x times more selective in inhibiting the Type II enzyme (present in hair follicles) than the Type I enzyme (present in other body tissues). The turnover (T1/2) of the finasteride/5AR Type II complex is 30 days and the finasteride/5AR Type I complex is 15 days. This explains why finasteride does not need to be taken every day and why, after stopping finasteride, the effects may take a month or longer to begin to disappear.

• Read about the first comprehensive study to investigate Propecia’s long term efficacy
• Read more about Propecia (finasteride)