Q: I heard that Propecia was being used originally for shrinking the prostate, is this true? — M.D., New Hyde Park, N.Y.

A: Propecia (finasteride 1mg) is not a prostate medication that was serendipitously noted to have a side effect of re-growing hair, it is a medication that was known all along that it might be able to slow hair loss and/or to grow hair.

Although finasteride was first approved for the treatment of prostate enlargement, the researchers at Merck knew, at the outset, that there were families whose members were deficient in the 5-alpha reductase Type II enzyme and that the men in these families neither developed prostate disease nor went bald. In addition they had no long-term problems from the lack of this enzyme.

Merck used this natural model to develop a medication that could block the 5-alpha reductase Type II enzyme – the result was finasteride. Because the only approved treatment for symptoms related to prostate enlargement at the time was surgery, Merck developed finasteride as a medical treatment for this condition prior to developing finasteride as a potential treatment for men with male pattern hair loss.

This also meant that Merck would understand the safety profile of finasteride, and have it approved for a medical disease (symptomatic prostate enlargement), before developing it for a cosmetic condition.

The drug was first submitted to the FDA for the treatment of prostate enlargement as Proscar (finasteride 5mg) in 1991 and it was approved for this use in 1992. The drug was submitted for the treatment of men with male pattern hair loss as Propecia (finasteride 1mg) in 1996 and was approved for this use in 1997.