Sildenafil, Oral Tablet

Medically reviewed by University of Illinois-Chicago, Drug Information Group on February 8, 2017Written by University of Illinois-Chicago, Drug Information Group

Important warnings

  • Priapism warning: This drug can cause priapism, which is an erection that won’t go away. If you have an erection that lasts more than 4 hours, call 911 or go to the nearest emergency room. If it’s not treated right away, this condition can cause permanent damage to your penis.
  • Sudden vision loss warning: This drug can cause sudden vision loss in one or both eyes. This can be a sign of a serious eye problem. If this occurs, stop taking sildenafil and call your doctor right away.
  • Sudden hearing loss warning: This drug can cause hearing loss, tinnitus (ringing in your ears), or dizziness. If you have sudden hearing loss with or without tinnitus or dizziness, stop taking sildenafil and call your doctor right away.
  • Use in children warning: Children with PAH who take this drug may be at increased risk of death. Children should not take sildenafil.

What is sildenafil?

Sildenafil is a prescription drug. It comes in the form of a tablet and suspension (liquid). Both are taken by mouth. It also comes in an intravenous (IV) form, which is only given by a doctor.

Sildenafil is available as a brand-name drug called Revatio. It’s also available as a generic drug. Generic drugs usually cost less than the brand-name version. In some cases, they may not be available in every strength or form as the brand-name drug.

Why it's used

Sildenafil is used to treat pulmonary arterial hypertension (PAH). With this condition, the blood pressure in your lungs is too high. Your heart has to work very hard to pump blood into your lungs.

This drug slows down how fast your illness worsens. It also makes you more able to exercise.

How it works

Sildenafil belongs to a class of drugs called phosphodiesterase type 5 (PDE5) inhibitors. A class of drugs is a group of medications that work in a similar way. These drugs are often used to treat similar conditions.

Sildenafil works by relaxing the muscles and opening up the blood vessels in your lungs. This decreases the blood pressure in your lungs.

Sildenafil side effects

Sildenafil oral tablet doesn’t cause drowsiness, but it can cause other side effects.

More common side effects

The more common side effects of sildenafil can include:

  • nosebleeds
  • headaches
  • upset stomach
  • flushing (reddening and warming of the face)
  • trouble sleeping
  • fever
  • an erection that lasts longer than normal
  • respiratory infection
  • nausea
  • vomiting
  • bronchitis
  • sore throat
  • runny nose

If these effects are mild, they may go away within a few days or a couple of weeks. If they’re more severe or don’t go away, talk to your doctor or pharmacist.

Serious side effects

Call your doctor right away if you have serious side effects. Call 911 if your symptoms feel life-threatening or if you think you’re having a medical emergency. Serious side effects and their symptoms can include the following:

  • Low blood pressure. Symptoms can include:
    • blurry vision
    • confusion
    • dizziness
    • fainting
    • lightheadedness
    • nausea or vomiting
    • sleepiness
    • weakness
  • Increased shortness of breath or trouble breathing
  • Priapism (an erection that won’t go away). Symptoms can include:
    • an erection that lasts more than 4 hours
  • Vision problems. Symptoms can include:
    • sudden vision loss in one or both eyes
  • Hearing problems. Symptoms can include:
    • sudden hearing loss
    • tinnitus (ringing in your ears)
    • dizziness
  • Heart problems, such as heart attack, stroke, or irregular heart rate. Symptoms can include:
  • chest pain
  • shortness of breath
  • dizziness
  • trouble speaking
  • confusion
  • nausea or vomiting
  • feeling lightheaded

Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs affect each person differently, we can not guarantee that this information includes all possible side effects. This information is not a substitute for medical advice. Always discuss possible side effects with a healthcare provider who knows your medical history.

Sildenafil may interact with other medications

Sildenafil oral tablet can interact with other medications, vitamins, or herbs you may be taking. An interaction is when a substance changes the way a drug works. This can be harmful or prevent the drug from working well.

To help avoid interactions, your doctor should manage all of your medications carefully. Be sure to tell your doctor about all medications, vitamins, or herbs you’re taking. To find out how this drug might interact with something else you’re taking, talk to your doctor or pharmacist.

Examples of drugs that can cause interactions with sildenafil are listed below.

Drugs you should not use with sildenafil

Do not take these drugs with sildenafil. Doing so can cause dangerous effects in the body. Examples of these drugs include:

  • Nitrates, such as isosorbide mononitrate, isosorbide dinitrate, or nitroglycerin.
    • Taking these drugs with sildenafil can cause your blood pressure to drop suddenly to an unsafe level.
  • Guanylate cyclase stimulators, such as riociguat.
    • Taking these drugs with sildenafil can cause your blood pressure to drop suddenly to an unsafe level.

Interactions that increase your risk of side effects

Side effects from sildenafil: Taking sildenafil with certain medications raises your risk of side effects from sildenafil. This is because the amount of sildenafil in your body is increased. Examples of these drugs include:

  • HIV drugs, such as ritonavir, indinavir, saquinavir, or atazanavir.
    • Increased side effects can include low blood pressure, dizziness, or vision problems. They can also include erections that last longer than normal.
  • Certain antibiotics, such as clarithromycin, telithromycin, or erythromycin.
    • Increased side effects can include low blood pressure, dizziness, or vision problems. They can also include erections that last longer than normal.
  • Certain antifungals, such as ketoconazole or itraconazole.
    • Increased side effects can include low blood pressure, dizziness, or vision problems. They can also include erections that last longer than normal.

Side effects from other drugs: Taking sildenafil with certain medications raises your risk of side effects from these drugs. Examples of these drugs include:

  • Alpha-blockers, such as terazosin, tamsulosin, doxazosin, alfuzosin, or silodosin.
    • Increased side effects can include a drop in blood pressure, or fainting.
  • Blood pressure drugs, such as amlodipine.
    • Increased side effects can include blood pressure that’s too low.
  • Drugs for erectile dysfunction, such as avanafil, tadalafil, or vardenafil.
    • Increased side effects can include low blood pressure or erections that last longer than normal.

    Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs interact differently in each person, we can not guarantee that this information includes all possible interactions. This information is not a substitute for medical advice. Always speak with your healthcare provider about possible interactions with all prescription drugs, vitamins, herbs and supplements, and over-the-counter drugs that you are taking.

Sildenafil warnings

This drug comes with several warnings.

Allergy warning

Sildenafil can cause a severe allergic reaction. Symptoms can include:

  • trouble breathing
  • swelling of your throat or tongue

If you develop these symptoms, call 911 or go to the nearest emergency room.

Don’t take this drug again if you’ve ever had an allergic reaction to it. Taking it again could be fatal (cause death).

Alcohol interaction warning

The use of drinks that contain alcohol raises your risk of low blood pressure from sildenafil. If you drink alcohol, talk to your doctor. You may need to have your blood pressure monitored while you take this drug.

Warnings for people with certain health conditions

For people with heart problems: This drug can lower your blood pressure. If you’ve had certain heart problems in the last 6 months, ask your doctor whether this drug is safe for you. These problems include a heart attack, stroke, or life-threatening heart rhythm problem. Also talk with your doctor if you have a low or high resting blood pressure, or a history of heart failure or coronary artery disease.

For people with pulmonary veno-occlusive disease (PVOD): Taking this drug may worsen your heart function. You should not take this drug.

For people with eye problems: This drug may cause sudden loss of vision in one or both eyes. This may be a sign of non-arteritic anterior ischemic optic neuropathy (NAION). If you’ve already had NAION or have crowded optic disc, you may have a higher risk of NAION and vision changes with this drug.

For people with problems with the shape of their penis: If you have a problem with the shape of your penis, such as Peyronie’s disease, this drug raises your risk of having an erection that lasts more than 4 hours.

For people with a history of stomach ulcers or bleeding: This drug raises your risk of stomach bleeding, ulcers, or small holes in the lining of your digestive system. These events can be fatal (cause death). They can happen at any time, with or without symptoms.

For people with sickle cell anemia: This drug may cause a common painful complication of sickle cell anemia called vaso-occlusive crisis. If you have sickle cell anemia, ask your doctor whether this drug is safe for you.

Warnings for other groups

For pregnant women: This drug is a category B pregnancy drug. That means two things:

  1. Research in animals has not shown a risk to the fetus when the mother takes the drug.
  2. There aren’t enough studies done in humans to show if the drug poses a risk to the fetus.

Talk to your doctor if you’re pregnant or planning to become pregnant. It appears unlikely that this drug will harm a pregnancy. However, this drug should only be used during pregnancy if clearly needed.

For women who are breastfeeding: This drug may pass into breast milk and may cause side effects in a child who is breastfed. Talk to your doctor if you breastfeed your child. You may need to decide whether to stop breastfeeding or stop taking this medication.

For seniors: The kidneys, liver, or heart of older adults may not work as well as they used to. This can cause your body to process drugs more slowly. As a result, a higher amount of a drug stays in your body for a longer time. This raises your risk of side effects.

For children: This drug isn’t recommended in children younger than 18 years of age. In one study, children with PAH who took this drug had an increased chance of death.

How to take sildenafil

All possible dosages and drug forms may not be included here. Your dosage, drug form, and how often you take the drug will depend on:

  • your age
  • the condition being treated
  • how severe your condition is
  • other medical conditions you have
  • how you react to the first dose

Dosage for pulmonary arterial hypertension (PAH)

Generic: Sildenafil

  • Form: oral tablet
  • Strengths: 20 mg

Brand: Revatio

  • Form: oral tablet
  • Strengths: 20 mg

Adult dosage (ages 18–64 years)

  • Typical dosage: 5 or 20 mg, taken 3 times per day.
  • Maximum dosage: 20 mg, taken 3 times per day.

Child dosage (ages 0–17 years)

This drug shouldn’t be used in children younger than 18 years of age.

Senior dosage (ages 65 years and older)

The kidneys, liver, or heart of older adults may not work as well as they used to. This can cause your body to process drugs more slowly. As a result, a higher amount of a drug stays in your body for a longer time. This raises your risk of side effects.

Your doctor may start you on a lowered dosage of sildenafil. This can help prevent levels of this drug from building up in your body.

Disclaimer: Our goal is to provide you with the most relevant and current information. However, because drugs affect each person differently, we can not guarantee that this list includes all possible dosages. This information is not a substitute for medical advice. Always speak with your doctor or pharmacist about dosages that are right for you.

Take as directed

Sildenafil oral tablet is used for long-term treatment. It comes with serious risks if you don’t take it as prescribed.

If you stop taking the drug suddenly or don’t take it at all: Your condition won’t improve, and may get worse. Also, you won’t be able to exercise.

If you miss doses or don’t take the drug on schedule: This medication may not work as well or may stop working completely. For this drug to work well, a certain amount needs to be in your body at all times.

If you take too much: You could have dangerous levels of the drug in your body. Symptoms of an overdose of this drug can include:

  • low blood pressure
  • fainting
  • dizziness
  • vision problems
  • hearing problems
  • upset stomach
  • chest pain

If you think you’ve taken too much of this drug, call your doctor or local poison control center. If your symptoms are severe, call 911 or go to the nearest emergency room right away.

What to do if you miss a dose: Take your dose as soon as you remember. But if you remember just a few hours before your next scheduled dose, take only one dose. Never try to catch up by taking two doses at once. This could result in dangerous side effects.

How to tell if the drug is working: You should be able to exercise more easily. Your doctor will also check you to determine if this drug is working.

Important considerations for taking sildenafil

Keep these considerations in mind if your doctor prescribes sildenafil for you.

General

  • You can take this drug with or without food.
  • Take this drug 3 times per day about 4–6 hours apart. Take it at the same times every day.
  • You can cut or crush the tablet.

Storage

  • Store sildenafil tablets at room temperature between 59°F and 86°F (15°C and 30°C).
  • Keep sildenafil tablets away from light.
  • Don’t store this medication in moist or damp areas, such as bathrooms.

Refills

A prescription for this medication is refillable. You should not need a new prescription for this medication to be refilled. Your doctor will write the number of refills authorized on your prescription.

Travel

When traveling with your medication:

  • Always carry your medication with you. When flying, never put it into a checked bag. Keep it in your carry-on bag.
  • Don’t worry about airport x-ray machines. They can’t harm your medication.
  • You may need to show airport staff the pharmacy label for your medication. Always carry the original prescription-labeled container with you.
  • Don’t put this medication in your car’s glove compartment or leave it in the car. Be sure to avoid doing this when the weather is very hot or very cold.

Clinical monitoring

Your doctor may monitor your blood pressure and pulse regularly.

Availability

Not every pharmacy stocks this drug. When filling your prescription, be sure to call ahead to make sure your pharmacy carries it.

Prior authorization

Many insurance companies require a prior authorization for this drug. This means your doctor may need to get approval from your insurance company before your insurance company will pay for the prescription.

Are there any alternatives?

There are other drugs available to treat your condition. Some may be better suited for you than others. Talk to your doctor about other drug options that may work for you.

Disclaimer: Healthline has made every effort to make certain that all information is factually correct, comprehensive, and up-to-date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or other healthcare professional before taking any medication. The drug information contained here in is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.

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