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Sildenafil Tablets: Patient Information And Q&A

Patient information and frequently asked questions about Sildenafil (generic Viagra) for ED.

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(Generic Viagra)

Disclaimer: The information provided on this page is not a substitute for professional medical advice, diagnosis, or treatment. If you have any questions or concerns about your health, please talk to a doctor.

What is Sildenafil?

Sildenafil is a PDE5 inhibitor that is most commonly used for erectile dysfunction or ED. Sildenafil is the active ingredient in Viagra. Sildenafil is also the active ingredient in a medication for pulmonary arterial hypertension (PAH) in a drug called Revatio.

What is Generic Viagra?

Sildenafil is the generic form of Viagra. Generic medications are required by the FDA to be bioequivalent to the brand medication, meaning that they act the same way in the body and have the same active ingredients. Generic medications also tend to be less expensive than the brand medications and most medications sold in the U.S. are generic.

How does Sildenafil work?

To get an erection, the body uses chemical signals that tell the vessels to open up and flood blood into the penis when mentally stimulated. Normally, the body then almost as quickly uses an enzyme (PDE-5) to break down those blood flow chemicals, causing blood to leave and the erection to go down. Sildenafil works by blocking the breakdown enzyme (PDE-5), to help maintain the blood flow and erection.

How should I take Sildenafil?

Take the dose directed by your doctor by mouth with some water 30 minutes to 4 hours before sexual activity (1 hour before is optimal). Do not take more than one dose daily. You may take your dose on an empty stomach or with food. Take only the amount of Sildenafil your doctor directed you to take, taking more Sildenafil than directed may cause an increased risk of side effects.

How long does Sildenafil take to work?

Most patients will start having a response from Sildenafil 20-30 minutes after taking their dose, although full effects may take longer. Eating a high-fat meal just before taking your dose may delay the time it takes for Sildenafil to work.

How long does Sildenafil last?

In most people, the effects of Sildenafil last about 2 hours. Even after the effects of the medication have worn off, the medication is still in your system for up to a day after dosing - so do not take more than one dose daily. If you find your dose lasting 4+ hours, seek medical attention as this is considered priapism and could have damaging effects on the tissues.

What should I tell my doctor before starting Sildenafil?

Before taking Sildenafil make sure your doctor knows about any of the following health conditions: Heart conditions, liver, kidney, eye conditions, bleeding disorders, or penile deformities. Also make sure your doctor knows about all of your current medications, supplements, and any other conditions.

What should I avoid while taking Sildenafil?

Drinking alcohol with Sildenafil can cause side effects including low blood pressure or dizziness. Grapefruit may interact with Sildenafil and lead to unwanted side effects. Avoid the use of grapefruit products. Avoid using any other medicines to treat impotence, such as alprostadil or yohimbine, without first talking to your doctor.

What are the common side effects of Sildenafil?

The common side effects of Sildenafil are: flushing (warmth, redness, or tingly feeling), headache, dizziness, heartburn, nausea, or upset stomach, abnormal vision (blurred vision, changes in color vision), runny or stuffy nose, nosebleeds, sleep problems (insomnia), muscle pain, back pain. For a full list of possible side effects see the important safety information below.

What if I overdose Sildenafil?

Taking too much Sildenafil can increase adverse side effects of the medication including severe side effects including extremely low blood pressure or having an erection for longer than 4 hours (priapism). If you have taken more than prescribed by your doctor, or you took the directed amount but you are still having these side effects, seek emergency medical attention.

Important Safety Information for Sildenafil


  • Do not take sildenafil if you are also using a nitrate drug for chest pain or heart problems, including nitroglycerin, isosorbide dinitrate, isosorbide mononitrate, and some recreational drugs such as "poppers". Taking sildenafil with a nitrate medicine can cause a sudden and serious decrease in blood pressure.
  • Some medicines can cause unwanted or dangerous effects when used with sildenafil. Tell your doctor about all your current medicines, especially riociguat (Adempas). Do not take sildenafil with riociguat.
  • Contact your doctor or seek emergency medical attention if your erection is painful or lasts longer than 4 hours. A prolonged erection (priapism) can damage the penis.
  • Stop using sildenafil and get emergency medical help if you have sudden vision loss. Sildenafil can decrease blood flow to the optic nerve of the eye, causing sudden vision loss. This has occurred in a small number of people taking sildenafil, most of whom also had heart disease, diabetes, high blood pressure, high cholesterol, or certain pre-existing eye problems, and in those who smoke or are over 50 years old. It is not clear whether this medicine is the actual cause of vision loss. Do not give this medication to anyone under 18 years old without medical advice.

Before taking this medication:

You should not use sildenafil if you are allergic to it, or:

  • If you take other medicines to treat pulmonary arterial hypertension, such as riociguat (Adempas).
  • If you are also using a nitrate drug for chest pain or heart problems. This includes nitroglycerin, isosorbide dinitrate, and isosorbide mononitrate. Nitrates are also found in some recreational drugs such as amyl nitrate or nitrite ("poppers"). Taking sildenafil with a nitrate medicine can cause a sudden and serious decrease in blood pressure.

To make sure sildenafil is safe for you, tell your doctor if you have ever had:

  • Heart problems (chest pain, a heart rhythm disorder, heart attack)
  • High or low blood pressure
  • Blood circulation problems
  • Retinitis pigmentosa (an inherited condition of the eye)
  • Blindness in one or both eyes
  • Bleeding problems
  • A stomach ulcer
  • Pulmonary veno-occlusive disease (PVOD)
  • Liver or kidney disease
  • A blood cell disorder such as sickle cell anemia, multiple myeloma, or leukemia
  • A physical deformity of the penis (such as Peyronie's disease)
  • If you have been told you should not have sexual intercourse for health reasons.

Drug Interactions:

  • Nitrates: Nitroglycerin, isosorbide dinitrate, isosorbide mononitrate, and some recreational drugs such as "poppers". Taking a nitrate medicine with Sildenafil can cause a dangerous decrease in blood pressure.
  • Guanylate cyclase stimulators: Adempas® (riociguat)
  • Alpha-blockers: Hytrin® (terazosin HCl), Flomax® (tamsulosin HCl), Cardura® (doxazosin mesylate), Minipress® (prazosin HCl), Uroxatral® (alfuzosin HCl), Jalyn® (dutasteride and tamsulosin HCl), or Rapaflo® (silodosin)
  • HIV protease inhibitors: ritonavir (Norvir®), indinavir sulfate (Crixivan®), saquinavir (Fortovase® or Invirase®), or atazanavir sulfate (Reyataz®)
  • Oral antifungal medicines: ketoconazole (Nizoral®) and itraconazole (Sporanox®)
  • Antibiotics: clarithromycin (Biaxin®), telithromycin (Ketek®), or erythromycin
  • Other medicines that treat high blood pressure
  • Other medicines or treatments for ED
  • Viagra® and generic Viagra® also contain sildenafil, sildenafil is also found in a drug called Revatio® used for pulmonary arterial hypertension (PAH). Do not use sildenafil with Viagra®, Revatio®, or with any other PDE5 inhibitor or erectile dysfunction treatment.

Side Effects:

Get emergency medical help if you have signs of an allergic reaction to sildenafil:

  • Hives, difficulty breathing, swelling of your face, lips, tongue, or throat.

Stop taking sildenafil and get emergency medical help if you have:

  • heart attack symptoms - chest pain or pressure, pain spreading to your jaw or shoulder, nausea, sweating
  • vision changes or sudden vision loss
  • erection is painful or lasts longer than 4 hours (prolonged erection can damage the penis)
  • ringing in your ears, or sudden hearing loss
  • irregular heartbeat
  • swelling in your hands, ankles, or feet
  • shortness of breath
  • seizure (convulsions)
  • a light-headed feeling, like you might pass out

Common sildenafil side effects may include:

  • flushing (warmth, redness, or tingly feeling)
  • headache, dizziness
  • heartburn, nausea, or upset stomach
  • abnormal vision (blurred vision, changes in color vision)
  • runny or stuffy nose, nosebleeds
  • sleep problems (insomnia)
  • muscle pain, back pain

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

Additional Resources

The following links provide further information on the potential risks and benefits of this medication:

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