If you're one of the 40 million US men with hereditary hair loss, there are two products available to help you grow and keep your hair. Finasteride (Propecia), which requires a doctor's prescription, and minoxidil (Rogaine), which has been available without a prescription since February 1996.

How Does Finasteride Work?

Finasteride was first developed to shrink enlarged prostate glands. Researchers noticed that it also helped grow hair, so a special lower-dose formulation—Propecia—was developed for hair loss.

It is how finasteride works that enthuses doctors familiar with the drug. Finasteride interferes with conversion of testosterone to another hormone called dihydro-testosterone (or DHT). DHT reduces hair follicle activity. Over time and under the influence of DHT, follicles sprout thinner hairs until no hair regrows. When finasteride blocks DHT production, thinning of hair ceases and a more normal growth may possibly occur.

Minoxidil's activity, in contrast, is thought to involve stimulation of hair follicles to become larger and make normal hairs.

The Good News and the Bad News

In clinical studies, approximately 20% of men taking the one milligram daily dose of Propecia grew moderate to heavy amounts of new hair after one year. Another 30% had less cosmetically apparent growth. These numbers inched up slightly when used for two years. And both Propecia and minoxidil work best in men who are losing hair on the top of their heads (instead of a receding hairline or frontal hair loss). Minoxidil also may lead to new hair production, but results are more variable because of individual inconsistencies in committing to a twice/daily program of applying the solution to the scalp.

But it isn't only Propecia's ability to grow hair that interests some doctors. There is evidence that Propecia can help men stop losing the hair they have. So it appears that even if Propecia doesn't help you grow lots of new hair, it's a good bet you'll keep what you have—at least for a while.

You must be patient, though, and be willing to take the drug once a day indefinitely. It may take 3-4 months before new hair is noticed. If you stop taking the drug, all your newly grown hair will fall out over time. The same is true with minoxidil.

There may be even more good news for the balding among us: the 2003 Prostate Cancer Prevention trial seems to have established that finasteride is effective in reducing prostate cancer risk. Since bald men may have somewhat increased risk of prostate cancer, finasteride treatment may offer benefits beyond just improving appearance.

Side Effects

Propecia has some potentially unsettling side effects. Propecia has been associated with a reduced sex drive, occasional impotence, and/or a smaller amount of ejaculate, but these side effects are not common and disappear when the drug is stopped. Comparatively, minoxidil's side effects most commonly include scalp itch or skin irritation.

Men taking the drug should alert their physicians. One effect of taking Propecia is that it will lower PSA, a compound produced by the body in the presence of a prostate cancer or just with increased age. Blood tests checking for PSA levels may be more difficult to interpret as a result. Of course men who have both hair loss and symptoms of prostate obstruction (hesitancy in urinating, diminished urinary stream, and others) may find these symptoms improved if they take finasteride because of baldness.

Finasteride or Minoxidil—or Both?

So, should you use finasteride or minoxidil? You may not need to choose. Some evidence suggests that the effectiveness of both medications used together is better than one used alone. But taking Propecia more than once per day or applying minoxidil more than twice a day will not lead to more hair growth.