Erectile dysfunction, sometimes called "impotence," is the repeated inability to get or keep an erection firm enough for sexual intercourse. The word "impotence" may also be used to describe other problems that interfere with sexual intercourse and reproduction, such as lack of sexual desire and problems with ejaculation or orgasm. Using the term erectile dysfunction makes it clear that those other problems are not involved.

Erectile dysfunction, or ED, can be a total inability to achieve erection, an inconsistent ability to do so, or a tendency to sustain only brief erections. These variations make defining ED and estimating its incidence difficult. Estimates range from 15 million to 30 million, depending on the definition used. According to the National Ambulatory Medical Care Survey (NAMCS), for every 1,000 men in the United States, 7.7 physician office visits were made for ED in 1985. By 1999, that rate had nearly tripled to 22.3. The increase happened gradually, presumably as treatments such as vacuum devices and injectable drugs became more widely available and discussing erectile function became accepted. Perhaps the most publicized advance was the introduction of the oral drug sildenafil citrate (Viagra) in March 1998. NAMCS data on new drugs show an estimated 2.6 million mentions of Viagra at physician office visits in 1999, and one-third of those mentions occurred during visits for a diagnosis other than ED.

In older men, ED usually has a physical cause, such as disease, injury, or side effects of drugs. Any disorder that causes injury to the nerves or impairs blood flow in the penis has the potential to cause ED. Incidence increases with age: About 5 percent of 40-year-old men and between 15 and 25 percent of 65-year-old men experience ED. But it is not an inevitable part of aging.

ED is treatable at any age, and awareness of this fact has been growing. More men have been seeking help and returning to normal sexual activity because of improved, successful treatments for ED.

Most physicians suggest that treatments proceed from least to most invasive. Cutting back on any drugs with harmful side effects is considered first. For example, drugs for high blood pressure work in different ways. If you think a particular drug is causing problems with erection, tell your doctor and ask whether you can try a different class of blood pressure medicine.

Drugs for treating ED can be taken orally, injected directly into the penis, or inserted into the urethra at the tip of the penis. In March 1998, the Food and Drug Administration (FDA) approved Viagra, the first pill to treat ED. In August 2003, the FDA gave approval to a second oral medicine, vardenafil hydrochloride (Levitra). Additional oral medicines are being tested for safety and effectiveness.

Taken an hour before sexual activity, Viagra and Levitra work by enhancing the effects of nitric oxide, a chemical that relaxes smooth muscles in the penis during sexual stimulation and allows increased blood flow.

While oral medicines improve the response to sexual stimulation, they do not trigger an automatic erection as injections do. The recommended dose for Viagra is 50 mg, and the physician may adjust this dose to 100 mg or 25 mg, depending on the patient. The recommended dose for Levitra is 10 mg, and the physician may adjust this dose to 20 mg if 10 mg is insufficient. Lower doses of 5 mg and 2.5 mg are available for patients who take other medicines or have conditions that may decrease the body's ability to use Levitra.

Neither Viagra nor Levitra should be used more than once a day. Men who take nitrate-based drugs such as nitroglycerin for heart problems should not use either drug because the combination can cause a sudden drop in blood pressure. Also, Levitra should not be taken with any of the drugs called alpha-blockers, which are used to treat prostate enlargement or high blood pressure.

Oral testosterone can reduce ED in some men with low levels of natural testosterone, but it is often ineffective and may cause liver damage. Patients also have claimed that other oral drugs—including yohimbine hydrochloride, dopamine and serotonin agonists, and trazodone—are effective, but the results of scientific studies to substantiate these claims have been inconsistent. Improvements observed following use of these drugs may be examples of the placebo effect, that is, a change that results simply from the patient's believing that an improvement will occur.

Many men achieve stronger erections by injecting drugs into the penis, causing it to become engorged with blood. Drugs such as papaverine hydrochloride, phentolamine, and alprostadil (marketed as Caverject) widen blood vessels. These drugs may create unwanted side effects, however, including persistent erection (known as priapism) and scarring. Nitroglycerin, a muscle relaxant, can sometimes enhance erection when rubbed on the penis.

A system for inserting a pellet of alprostadil into the urethra is marketed as Muse. The system uses a prefilled applicator to deliver the pellet about an inch deep into the urethra. An erection will begin within 8 to 10 minutes and may last 30 to 60 minutes. The most common side effects are aching in the penis, testicles, and area between the penis and rectum; warmth or burning sensation in the urethra; redness from increased blood flow to the penis; and minor urethral bleeding or spotting.

Research on drugs for treating ED is expanding rapidly. Patients should ask their doctor about the latest advances.