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Harvard Commentaries
Harvard Commentaries
Reviewed by the Faculty of Harvard Medical School

Man to Man Man to Man

Erectile Dysfunction (ED)

January 24, 2013

By Harvey B. Simon M.D.

Harvard Medical School

Until sildenafil (Viagra) burst on the scene in 1998, erectile dysfunction (ED) was called "impotence." Few men faced up to the problem. All that has changed. We now know that ED is a medical problem, not a personal failure. We also know that men should discuss ED with their doctors, rather than hide it because of embarrassment. Above all, we know that ED is treatable.

What Causes ED?

Every man has erectile failure from time to time. But doctors diagnose ED when a man can't maintain an erection adequate for intercourse on at least 25% of attempts.

Doctors used to think psychological problems were the main cause of ED. In fact, less than 15% of cases have an emotional basis. If a man has normal erections during sleep but not during sex, chances are the problem is psychological.

Many men blame ED on aging, but it's not the culprit. ED is usually the result of illnesses that develop in older men. Here are the major causes of ED:

  • Vascular diseases – Atherosclerosis ("hardening of the arteries"), high blood pressure
  • Metabolic disorders – Diabetes, obesity
  • Neurological disorders – Spinal cord problems
  • Endocrine disorders – Problems of the pituitary gland and testicles
  • Prostate problems – Treatment of prostate cancer
  • Medications – Drugs for blood pressure, cholesterol, depression, anxiety and ulcers
  • Lifestyle factors – Smoking, alcohol abuse, lack of exercise, substance abuse

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The Medical Evaluation

Erectile dysfunction and heart disease share many risk factors, such as high blood pressure, high cholesterol, diabetes, smoking, obesity and lack of exercise. That's why evaluating heart health in a man who may have ED is very important. In fact, many men who see a doctor for ED will be back with heart disease unless risk factors are diagnosed and treated.

A 2005 American study shows that ED is a health problem. The study followed 8,063 men ages 55 and older for eight years. When the study began in 1994, none of the men had diagnosed coronary artery disease, but 3,816 (47%) had ED. Another 2,420 (30%) developed ED over the next five years. By the end of the study, the men with ED were one and a half times more likely to develop signs of heart disease than the men who had normal erectile function.

The doctor should evaluate a man's general health and then his prostate. Some doctors will test testosterone and other hormone levels in the blood, but usually these tests aren't informative. And although urologists can do additional tests, they rarely help. That's because in most cases, a trial of treatment comes next.

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Treatment: Medications

If a doctor knows the cause of ED, the first step is to treat that cause. For example, if it's a side effect of medication, the doctor should switch to another drug. Even if no correctable problem is found, all men should begin to work on risk factors, such as smoking, high blood pressure and obesity that contribute to ED. It's important, but should not delay a trial of treatment with medication.

In addition to sildenafil, there are two other oral medications that are effective for treating ED: Vardenafil (Levitra) and tadalafil (Cialis). Although you'd never guess by the ads, the three pills are very similar. They boost a chemical that widens the arteries in the penis so blood flow increases. They don't cause erections by themselves. They only improve the response to sexual stimulation.





Tablet strengths
25, 50, 100 mg
2.5, 5, 10, 20 mg
2.5, 5, 10, 20 mg
Effect of food
Delayed or impaired absorption, especially with high-fat foods
Onset of action
30-60 minutes
15-30 minutes
30-45 minutes
Duration of action
4 hours (sometimes up to 12 hours)
4 hours (sometimes up to 12 hours)
36 hours
Drug interactions
Cannot take nitroglycerin for 24 hours after using
Cannot take nitroglycerin for 24 hours after using
Cannot take nitroglycerin for 48 hours after using

ED medications help about 70% of men. However, only about 50% of diabetics and an even smaller percentage of prostate cancer survivors find them effective.

Although sildenafil, vardenafil and tadalafil are generally safe, they should not be used by men who:

  • Take nitroglycerin or other nitrate medication
  • Have unstable or advanced cardiovascular

Doctors should be cautious prescribing ED pills for men who take alpha-blocker medications, which are frequently prescribed for benign prostatic hyperplasia (BPH) and occasionally for high blood pressure. All men should be alert for side effects such as headache, facial flushing, lightheadedness, nausea, visual disturbances and hearing loss.

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Other Treatment Options

Men who can't take or don't respond to one of the three ED pills shouldn't be tempted by unregulated supplements. While most family doctors prescribe ED pills, the treatments below are usually given under the care of a urologist.


Alprostadil Injections

Alprostadil Pellets

Vacuum Pump

Onset of Action
5-15 minutes
5-15 minutes
Duration of Action
60 minutes
30-60 minutes
While in use
Up to 80% effective
About 50% effective
Doesn't need a prescription; up to 90% effective; no serious side effects
Injections require training and may be unpleasant for many men; may cause pain or painful sustained erections
Requires training; may cause mild pain and dizziness
Requires training; cumbersome; may cause numbness or bruising of the penis

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The Bottom Line

Erectile dysfunction is a medical problem. Your doctor should check for diabetes, vascular disease, hormonal abnormalities, psychological issues or a less common cause of ED. Work to control your risk factors related to lifestyle, such as smoking, obesity and diabetes. You may be asked to change medications that can cause ED. And in many cases, the next step is not more tests but a treatment trial, first with an ED pill.

According to a 2007 survey, about 18 million American men have ED. After many years of distress and disappointment, good treatments are finally available. But to enjoy the benefits of treatment to their fullest, ED treatment has to be part of a comprehensive program for heart and metabolic health.

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Harvey B. Simon, M.D. is an Associate Professor of Medicine at Harvard Medical School and a member of the Health Sciences Technology Faculty at Massachusetts Institute of Technology. He is the founding editor of the Harvard Men's Health Watch newsletter and author of six consumer health books, including The Harvard Medical School Guide to Men's Health (Simon and Schuster, 2002) and The No Sweat Exercise Plan, Lose Weight, Get Healthy and Live Longer (McGraw-Hill, 2006). Dr. Simon practices at the Massachusetts General Hospital; he received the London Prize for Excellence in Teaching from Harvard and MIT.

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