Finasteride (Propecia)

Men
This is a lower-dose version of a drug that shrinks prostates in middle-aged men. Propecia is available by prescription and is taken once a day. Propecia does grow and thicken hair to some extent, but its main use is to keep hair that's still there. It's therefore best for men who still have enough hair to retain. One side effect is impotence, but this is no more common than it is in the general population and is reversible when the drug is stopped. Taking Propecia once a day is easier that applying Rogaine, but the prospect of taking a pill daily for years doesn't sit well with some men.
Women
Propecia is a drug that helps men retain their hair. It is unsafe for women of childbearing age to take this drug or even handle tablets. It is, however, safe for their husbands to take it while they are trying to become pregnant. Propecia is safe for older women but may not be very effective.