If you are a man with hereditary hair loss, there are products available to help you keep your hair: finasteride (Propecia), which requires a prescription, and minoxidil (Rogaine), which is available over-the-counter.

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.

Finasteride interferes with conversion of testosterone to another hormone called 5 alpha-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 finasteride 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 finasteride 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 may be more variable because of individual inconsistencies in committing to a twice/daily program of applying the solution to the scalp.

But, it is not only finasteride's ability to grow hair that interests some doctors. There is evidence that finasteride can help men stop losing the hair they have. So it appears that even if finasteride does not help you grow lots of new hair, it is a good bet you will 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 of your newly grown hair will fall out over time.

Side Effects

Finasteride has some potentially unsettling side effects. The medicine has been associated with a reduced sex drive, occasional impotence, a smaller amount of ejaculate, and breast enlargement. But, these side effects are not common and disappear when the drug is stopped.

If you are taking the medicine, be sure that your doctors know. One effect of taking finasteride 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 the medicine being in your system. If you have both hair loss and symptoms of prostate enlargement (hesitancy in urinating, diminished urinary stream, and others), you may find that these symptoms improve because the medicine is also used to treat benign prostatic hypertrophy.

If you have hereditary hair loss, there are treatment options available. Talk to your doctor about whether you are a good candidate to take finasteride.