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
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. Urologists, who specialize in problems
of the urinary tract, have traditionally treated ED; however, urologists
accounted for only 25 percent of Viagra mentions in 1999.
How does an erection occur?
The penis contains two chambers called the corpora cavernosa, which run the
length of the organ (see figure 1). A spongy tissue fills the chambers. The
corpora cavernosa are surrounded by a membrane, called the tunica albuginea. The
spongy tissue contains smooth muscles, fibrous tissues, spaces, veins, and
arteries. The urethra, which is the channel for urine and ejaculate, runs along
the underside of the corpora cavernosa and is surrounded by the corpus
Erection begins with sensory or mental stimulation, or both. Impulses from
the brain and local nerves cause the muscles of the corpora cavernosa to relax,
allowing blood to flow in and fill the spaces. The blood creates pressure in the
corpora cavernosa, making the penis expand. The tunica albuginea helps trap the
blood in the corpora cavernosa, thereby sustaining erection. When muscles in the
penis contract to stop the inflow of blood and open outflow channels, erection
What causes ED?
Since an erection requires a precise sequence of events, ED can occur when
any of the events is disrupted. The sequence includes nerve impulses in the
brain, spinal column, and area around the penis, and response in muscles,
fibrous tissues, veins, and arteries in and near the corpora cavernosa.
Damage to nerves, arteries, smooth muscles, and fibrous tissues, often as a
result of disease, is the most common cause of ED. Diseases—such as diabetes,
kidney disease, chronic alcoholism, multiple sclerosis, atherosclerosis,
vascular disease, and neurologic disease—account for about 70 percent of ED
cases. Between 35 and 50 percent of men with diabetes experience ED.
Also, surgery (especially radical prostate and bladder surgery for cancer)
can injure nerves and arteries near the penis, causing ED. Injury to the penis,
spinal cord, prostate, bladder, and pelvis can lead to ED by harming nerves,
smooth muscles, arteries, and fibrous tissues of the corpora cavernosa.
In addition, many common medicines—blood pressure drugs, antihistamines,
antidepressants, tranquilizers, appetite suppressants, and cimetidine (an ulcer
drug)—can produce ED as a side effect.
Experts believe that psychological factors such as stress, anxiety, guilt,
depression, low self-esteem, and fear of sexual failure cause 10 to 20 percent
of ED cases. Men with a physical cause for ED frequently experience the same
sort of psychological reactions (stress, anxiety, guilt, depression).
Other possible causes are smoking, which affects blood flow in veins and
arteries, and hormonal abnormalities, such as not enough testosterone.
How is ED diagnosed?
Medical and sexual histories help define the degree and nature of ED. A
medical history can disclose diseases that lead to ED, while a simple recounting
of sexual activity might distinguish among problems with sexual desire,
erection, ejaculation, or orgasm.
Using certain prescription or illegal drugs can suggest a chemical cause,
since drug effects account for 25 percent of ED cases. Cutting back on or
substituting certain medications can often alleviate the problem.
A physical examination can give clues to systemic problems. For example, if
the penis is not sensitive to touching, a problem in the nervous system may be
the cause. Abnormal secondary sex characteristics, such as hair pattern or
breast enlargement, can point to hormonal problems, which would mean that the
endocrine system is involved. The examiner might discover a circulatory problem
by observing decreased pulses in the wrist or ankles. And unusual
characteristics of the penis itself could suggest the source of the problem—for
example, a penis that bends or curves when erect could be the result of
Several laboratory tests can help diagnose ED. Tests for systemic diseases
include blood counts, urinalysis, lipid profile, and measurements of creatinine
and liver enzymes. Measuring the amount of free testosterone in the blood can
yield information about problems with the endocrine system and is indicated
especially in patients with decreased sexual desire.
Monitoring erections that occur during sleep (nocturnal penile tumescence)
can help rule out certain psychological causes of ED. Healthy men have
involuntary erections during sleep. If nocturnal erections do not occur, then ED
is likely to have a physical rather than psychological cause. Tests of nocturnal
erections are not completely reliable, however. Scientists have not standardized
such tests and have not determined when they should be applied for best
A psychosocial examination, using an inter