Phosphodiesterase-5 Inhibitors (PDE-5 Inhibitors) for Erection Problems

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Phosphodiesterase-5 Inhibitors (PDE-5 Inhibitors) for Erection Problems


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Phosphodiesterase-5 inhibitors (PDE-5 inhibitors) are taken before you plan to be sexually active. PDE-5 inhibitors will result in an erection only if you are sexually stimulated.

How It Works

During an erection, blood fills tissue in the penis, causing it to enlarge and become stiff. The PDE-5 inhibitors relax smooth muscle, allowing the penis to fill with blood.

Why It Is Used

PDE-5 inhibitors can be used when an erection problem (erectile dysfunction) is caused by:

  • Diabetes.
  • High blood pressure.
  • Spinal cord injury or other problems affecting nerve function.
  • Prostate surgery.
  • Side effects of medicines.
  • Emotional or psychological causes.

How Well It Works

All PDE-5 inhibitors are very effective in treating erection problems, no matter what is causing the erection problem.

How well the PDE-5 inhibitors work depends on the person taking it and how much he takes. But these medicines seem to work in about 8 out of 10 men who use them for erection problems.1

The medicine needs to be taken before you plan to have sex:

  • Sildenafil (Viagra) starts to work as soon as 30 minutes and up to 4 hours after you take a pill.
  • Vardenafil (Levitra) starts to work as soon as 30 minutes and up to 4 hours after you take a pill.
  • Tadalafil (Cialis) starts to work as soon as 20 minutes and up to 36 hours after you take a pill.

Side Effects

Do not take PDE-5 inhibitors if you are taking any medicines that contains nitrates, such as nitroglycerin. This combination can lower blood pressure dangerously, possibly leading to a stroke, a heart attack, or death. If you are taking a medicines called an alpha-blocker—used to treat high blood pressure or an enlarged prostate—check with your doctor before you take a PDE-5 medicines.

Side effects may include:

  • Headache.
  • Skin flushing.
  • Indigestion.
  • Nasal congestion.

Some men taking a PDE-5 inhibitor find that the medicine affects their vision for a few hours after they take it, usually by causing a slight bluish tinge to their vision. A few men become more sensitive to light. These effects go away in a few hours.

Some men taking PDE-5 inhibitors have had sudden hearing loss, usually only in one ear. This loss of hearing may be related to the medicine. The U.S. Food and Drug Administration (FDA) advises any man taking a PDE-5 inhibitor who has sudden hearing loss to stop taking the medicine and call a doctor immediately. The hearing loss may be reversible.

Sildenafil (Viagra), tadalafil (Cialis), and vardenafil (Levitra) may be linked to a rare type of vision loss. If you experience sudden vision loss or vision-related problems while taking these drugs, Health Canada advises you to stop taking the drug and seek medical care immediately. If you already have eye disease or vision problems (such as cataracts, glaucoma, or retinopathy), be sure to speak with your eye doctor (ophthalmologist) before you start taking any PDE-5 inhibitors.

See Drug Reference for a full list of side effects. (Drug Reference is not available in all systems.)

What To Think About

Talk with your doctor about whether medicines for erection problems are safe for you if you:

Sexual activity is exercise. If you have a heart condition and have not been sexually active for a while, talk with your doctor to make sure you can safely engage in sexual activity.

PDE-5 inhibitors are not prescribed for anyone who may take nitroglycerin in an emergency.

Tell your doctor if you are using PDE-5 inhibitors and are going to have a test for heart disease (such as a stress treadmill test, cardiac catheterization, stress thallium, or stress echocardiography). Do not take sildenafil (Viagra) or vardenafil (Levitra) for 24 hours before the test. Do not take tadalafil (Cialis) for at least 48 hours before the test. Then if you have a problem during the test, it will be safe for you to use nitrate-containing medicines such as nitroglycerin.

If you eat a high-fat meal around the time you take sildenafil (Viagra) or vardenafil (Levitra), the medicine does not work as well as it otherwise would. So many doctors recommend you take this medicine on an empty stomach. Tadalafil (Cialis) works without regard to what you eat.

When considering PDE-5 inhibitors for erection problems, it is important to include your partner in your discussions.

If you take any medicines, discuss PDE-5 inhibitors with your doctor before using them.

PDE-5 inhibitors can be prescribed by any doctor. You do not have to see a doctor who specializes in sexual health. PDE-5 inhibitors are also available on the Internet. If you obtain the medicine through this route, you should discuss its use with your doctor.

PDE-5 inhibitors may affect fertility. If you are trying to have a child, you may want to ask your doctor about how this medicine can affect your chances of conceiving.

Complete the new medication information form (PDF) (What is a PDF document?) to help you understand this medication.



  1. Lue TF, Broderick GA (2007). Evaluation and nonsurgical management of erectile dysfunction and premature ejaculation. In AJ Wein, ed., Campbell-Walsh Urology, 9th ed., vol. 1, pp. 750–787. Philadelphia: Saunders Elsevier.


By Healthwise Staff
Primary Medical Reviewer E. Gregory Thompson, MD - Internal Medicine
Primary Medical Reviewer Andrew Swan, MD, CCFP, FCFP - Family Medicine
Specialist Medical Reviewer Christopher G. Wood, MD, FACS - Urology, Oncology
Last Revised July 13, 2010

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