Q Do Rogaine and Propecia work synergistically? — N.W., Chappaqua, N.Y.

A: They are synergistic, since the mechanisms of action are different.

Rogaine directly stimulates hair growth, while Propecia is permissive for hair growth by blocking DHT, the byproduct of testosterone that causes hair to miniaturize and eventually disappear.

The important thing to remember, however, is that for most people, Propecia is far more effective.