Erectile 

Dysfunction 

National Kidney and Urologic Diseases Information Clearinghouse 

National 

Institute of 

Diabetes and 

Digestive 

and Kidney 

Diseases 

NATIONAL 

INSTITUTES 

OF HEALTH 

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. 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. 

U.S. Department 

of Health and 

Human Services 
Dorsal artery 

Cavernous artery 

Bulbourethral artery Corpus spongiosum 

Deep dorsal vein 

Corpora cavernosa 

Bulbourethral vein Corpus spongiosum 

Corpora cavernosa 

Figure 1. Arteries (top) and veins (bottom) penetrate the long, filled 

cavities running the length of the penis—the corpora cavernosa and the 

corpus spongiosum. Erection occurs when relaxed muscles allow the 

corpora cavernosa to fill with excess blood fed by the arteries, while 

drainage of blood through the veins is blocked. 

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 is reversed. 

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. 

Lifestyle choices that contribute to heart 

disease and vascular problems also raise 

the risk of erectile dysfunction. Smoking, 

being overweight, and avoiding exercise are 

possible causes of ED. 

Also, surgery (especially radical prostate 

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. 

2 Erectile Dysfunction 
How is ED diagnosed? 

Patient History 

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 between 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. 

Physical Examination 

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, 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 

Peyronie’s disease. 

Laboratory Tests 

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 testosterone in the blood can yield information 

about problems with the endocrine system 

and is indicated especially in patients with 

decreased sexual desire. 

Other Tests 

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 results. 

Psychosocial Examination 

A psychosocial examination, using an 

interview and a questionnaire, reveals 

psychological factors. A man’s sexual partner may also be interviewed to determine 

expectations and perceptions during sexual 

intercourse. 

How is ED treated? 

Most physicians suggest that treatments 

proceed from least to most invasive. For 

some men, making a few healthy lifestyle 

changes may solve the problem. Quitting 

smoking, losing excess weight, and increasing physical activity may help some men 

regain sexual function. 

Cutting back on any drugs with harmful 

side effects is considered next. 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. 

Psychotherapy and behavior modifications 

in selected patients are considered next 

if indicated, followed by oral or locally 

injected drugs, vacuum devices, and surgically implanted devices. In rare cases, 

surgery involving veins or arteries may 

be considered. 

3 Erectile Dysfunction 
Psychotherapy 

Experts often treat psychologically based 

ED using techniques that decrease the 

anxiety associated with intercourse. The 

patient’s partner can help with the techniques, which include gradual development 

of intimacy and stimulation. Such techniques also can help relieve anxiety when 

ED from physical causes is being treated. 

Drug Therapy 

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. Since that time, vardenafil 

hydrochloride (Levitra) and tadalafil 

(Cialis) have also been approved. Additional oral medicines are being tested for 

safety and effectiveness. 

Viagra, Levitra, and Cialis all belong to a 

class of drugs called phosphodiesterase 

(PDE) inhibitors. Taken an hour before 

sexual activity, these drugs 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 either Levitra 

or Cialis is 10 mg, and the physician may 

adjust this dose to 20 mg if 10 mg is insufficient. A lower dose of 5 mg is available for 

patients who take other medicines or have 

conditions that may decrease the body’s 

ability to use the drug. Levitra is also available in a 2.5 mg dose. 

None of these PDE inhibitors 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, tell 

your doctor if you take any drugs called 

alpha-blockers, which are used to treat 

prostate enlargement or high blood pressure. Your doctor may need to adjust your 

ED prescription. Taking a PDE inhibitor 

and an alpha-blocker at the same time 

(within 4 hours) can cause a sudden drop 

in 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. 

4 Erectile Dysfunction 
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. 

Vacuum Devices 

Mechanical vacuum devices cause erection 

by creating a partial vacuum, which draws 

blood into the penis, engorging and 

expanding it. The devices have three 

components: a plastic cylinder, into 

which the penis is placed; a pump, which 

draws air out of the cylinder; and an elastic 

band, which is placed around the base of 

a 

c 

b 

Figure 2. A vacuum-constrictor device causes an 

erection by creating a partial vacuum around the penis, 

which draws blood into the corpora cavernosa. Pictured 

here are the necessary components: (a) a plastic cylinder, 

which covers the penis; (b) a pump, which draws air out 

of the cylinder; and (c) an elastic ring, which, when 

fitted over the base of the penis, traps the blood and 

sustains the erection after the cylinder is removed. 

5	 Erectile Dysfunction 

the penis to maintain the erection after the 

cylinder is removed and during intercourse 

by preventing blood from flowing back into 

the body (see figure 2). 

One variation of the vacuum device 

involves a semirigid rubber sheath that is 

placed on the penis and remains there after 

erection is attained and during intercourse. 

Surgery 

Surgery usually has one of three goals: 

•	 to implant a device that can cause the 

penis to become erect 

•	 to reconstruct arteries to increase


blood flow to the penis


•	 to block off veins that allow blood to 

leak from the penile tissues 

Implanted devices, known as prostheses, 

can restore erection in many men with ED. 

Possible problems with implants include 

mechanical breakdown and infection, 

although mechanical problems have diminished in recent years because of technological advances. 

Malleable implants usually consist of paired 

rods, which are inserted surgically into the 

corpora cavernosa. The user manually 

adjusts the position of the penis and, therefore, the rods. Adjustment does not affect 

the width or length of the penis. 

Inflatable implants consist of paired cylinders, which are surgically inserted inside 

the penis and can be expanded using pressurized fluid (see figure 3). Tubes connect 

the cylinders to a fluid reservoir and a 

pump, which are also surgically implanted. 

The patient inflates the cylinders by pressing on the small pump, located under the 

skin in the scrotum. Inflatable implants can 

expand the length and width of the penis 

somewhat. They also leave the penis in a 

more natural state when not inflated. 
a 

c 

b 

Figure 3. With an inflatable implant, erection is 

produced by squeezing a small pump (a) implanted in 

the scrotum. The pump causes fluid to flow from a 

reservoir (b) residing in the lower pelvis to two cylinders 

(c) residing in the penis. The cylinders expand to create 

the erection. 

Surgery to repair arteries can reduce ED 

caused by obstructions that block the flow 

of blood. The best candidates for such surgery are young men with discrete blockage 

of an artery because of an injury to the 

crotch or fracture of the pelvis. The procedure is less successful in older men 

with widespread blockage. 

Surgery to veins that allow blood to leave 

the penis usually involves an opposite procedure—intentional blockage. Blocking off 

veins (ligation) can reduce the leakage of 

blood that diminishes the rigidity of the 

penis during erection. However, experts 

have raised questions about the long-term 

effectiveness of this procedure, and it is 

rarely done. 

Hope Through Research 

Advances in suppositories, injectable medications, implants, and vacuum devices have 

expanded the options for men seeking 

treatment for ED. These advances have 

also helped increase the number of men 

seeking treatment. Gene therapy for ED is 

now being tested in several centers and may 

offer a long-lasting therapeutic approach 

for ED. 

The National Institute of Diabetes and 

Digestive and Kidney Diseases (NIDDK) 

sponsors programs aimed at understanding 

the causes of erectile dysfunction and 

finding treatments to reverse its effects. 

NIDDK’s Division of Kidney, Urologic, 

and Hematologic Diseases supported the 

researchers who developed Viagra and 

continue to support basic research into the 

mechanisms of erection and the diseases 

that impair normal function at the cellular 

and molecular levels, including diabetes 

and high blood pressure. 

6 Erectile Dysfunction 
For More Information 

American Urological Association (AUA) 

1000 Corporate Boulevard 

Linthicum, MD 21090 

Phone: 1–866–RING–AUA (746–4282) 

or 410–689–3700 

Fax: 410–689–3800 

Email: aua@auanet.org 

Internet: www.auanet.org 

www.urologyhealth.org 

AUA can refer you to a urologist in your 

area. 

American Diabetes Association (ADA) 

Attn: National Call Center 

1701 North Beauregard Street 

Alexandria, VA 22311 

Phone: 1–800–DIABETES (342–2383) 

Internet: www.diabetes.org 

ADA can help you find a doctor who specializes in diabetes care in your area. 

American Association of Sex Educators, 

Counselors, and Therapists (AASECT) 

P.O. Box 1960

Ashland, VA 23005–1960 

Phone: 804–752–0026 

Fax: 804–752–0056 

Internet: www.aasect.org 

Check the AASECT website to find a 

certified sexuality educator, counselor, 

or therapist in your area. 

• Erectile dysfunction (ED) is the 

repeated inability to get or keep an 

erection firm enough for sexual 

intercourse. 

• ED affects 15 to 30 million 

American men. 

• ED usually has a physical cause. 

• ED is treatable at all ages. 

• 

drug therapy, vacuum devices, and 

surgery. 

Points to Remember 

Treatments include psychotherapy, 

The U.S. Government does not endorse or 

favor any specific commercial product or 

company. Trade, proprietary, or company 

names appearing in this document are used 

only because they are considered necessary 

in the context of the information provided. 

If a product is not mentioned, the omission 

does not mean or imply that the product is 

unsatisfactory. 

7 Erectile Dysfunction 
National Kidney and 

Urologic Diseases 

Information Clearinghouse 

3 Information Way


Bethesda, MD 20892–3580


Phone: 1–800–891–5390


Fax: 703–738–4929


Email: nkudic@info.niddk.nih.gov


Internet: www.kidney.niddk.nih.gov


The National Kidney and Urologic Diseases 

Information Clearinghouse (NKUDIC) is a 

service of the National Institute of Diabetes and 

Digestive and Kidney Diseases (NIDDK). The 

NIDDK is part of the National Institutes 

of Health under the U.S. Department of Health 

and Human Services. Established in 1987, the 

Clearinghouse provides information about diseases of the kidneys and urologic system to 

people with kidney and urologic disorders and 

to their families, health care professionals, and 

the public. The NKUDIC answers inquiries, 

develops and distributes publications, and works 

closely with professional and patient organizations and Government agencies to coordinate 

resources about kidney and urologic diseases. 

Publications produced by the Clearinghouse are 

carefully reviewed by both NIDDK scientists 

and outside experts. This fact sheet was reviewed 

by Arnold Melman, M.D., Montefiore Medical 

Center, Bronx, NY; and Mark Hirsch, M.D., 

U.S. Food and Drug Administration. 

This publication is not copyrighted. The 

Clearinghouse encourages users of this fact 

sheet to duplicate and distribute as many 

copies as desired. 

This fact sheet is also available at 

www.kidney.niddk.nih.gov. 

U.S. DEPARTMENT OF HEALTH 

AND HUMAN SERVICES 

National Institutes of Health 

NIH Publication No. 06–3923 

December 2005