Sildenafil (Revatio, Viagra) is a generic prescription medication used to treat erectile dysfunction and pulmonary arterial hypertension in adults.

Sildenafil, which is also called sildenafil citrate, comes as an oral tablet. The drug also comes as an oral liquid suspension and IV infusion. However, this article does not cover these forms. It only covers the side effects of sildenafil oral tablets. If you’d like to learn more about these forms, talk with your doctor.

As with other drugs, sildenafil can cause side effects (adverse effects). It’s typically taken as a long-term treatment.

Read on to learn about potential common, mild, and serious side effects. For a general overview of sildenafil, including details about its uses, refer to this article. Your doctor can also tell you more about sildenafil.

Sildenafil can cause certain side effects, some of which are more common than others. These side effects may be temporary, lasting a few days to weeks. However, if the side effects last longer than that, bother you, or become severe, be sure to talk with your doctor or pharmacist.

These are just a few of the more common side effects reported by people who took sildenafil in clinical trials:*

  • flushing
  • upset stomach
  • blurry vision
  • headache†
  • nosebleeds†

* To learn more about the clinical trials of sildenafil, refer to the drug’s prescribing information for erectile dysfunction and pulmonary arterial hypertension.
† For more information about this side effect, see “Sildenafil: Side effect specifics” below.

Mild side effects can occur with sildenafil use. This list doesn’t include all possible mild side effects of the drug. For more information, you can refer to sildenafil’s prescribing information for erectile dysfunction (ED) and pulmonary arterial hypertension (PAH).

Mild side effects that have been reported with sildenafil include:

These side effects may be temporary, lasting a few days to weeks. However, if the side effects last longer than that, bother you, or become severe, be sure to talk with your doctor or pharmacist.

Note: After the Food and Drug Administration (FDA) approves a drug, it tracks and reviews side effects of the medication. If you develop a side effect while taking sildenafil and want to tell the FDA about it, visit MedWatch.

* For more information about this side effect, see “Sildenafil: Side effect specifics” below.
† An allergic reaction is possible after taking sildenafil. However, this side effect was rarely reported in clinical trials of sildenafil for ED and PAH. To learn more, see the “Sildenafil: Side effect specifics” section below.

Sildenafil may cause serious side effects. The list below may not include all possible serious side effects of the drug. For more information, you can refer to sildenafil’s prescribing information for erectile dysfunction (ED) and pulmonary arterial hypertension (PAH).

If you develop serious side effects while taking sildenafil, call your doctor right away. If the side effects seem life threatening or you think you’re having a medical emergency, immediately call 911 or your local emergency number.

Serious side effects that have been reported and their symptoms include:

* To learn more about this side effect, see the “Sildenafil: Side effect specifics” section below.
† An allergic reaction is possible after taking sildenafil. However, this side effect was rarely reported in clinical trials of sildenafil for ED and PAH. To learn more, see the “Sildenafil: Side effect specifics” section below.

Sildenafil is not approved by the Food and Drug Administration (FDA) for use in children. In clinical trials, children who were given sildenafil long term to treat pulmonary arterial hypertension had an increased risk of fatality.

However, your child’s doctor may recommend taking sildenafil off-label in some cases. (With off-label use, a doctor prescribes an FDA-approved drug for a purpose other than what it’s approved for.)

Talk with your child’s doctor to determine if sildenafil is right for your child. They can help compare the risks and benefits of the drug.

Sildenafil oral tablets come in different strengths: 20 milligrams (mg), 25 mg, 50 mg, and 100 mg. The dosage you’re prescribed will depend on what condition you’re taking sildenafil for. It also depends on how the dosage is working for you.

You can experience mild or severe side effects from sildenafil with any dosage. However, you may have an increased risk of side effects with higher dosages.

If you start to experience side effects that become bothersome or severe while taking sildenafil, talk with your doctor.

Sildenafil may cause several side effects. Here are some frequently asked questions about the drug’s side effects and their answers.

Are there reviews from people who had side effects with 50-mg or 100-mg sildenafil tablets?

No, there aren’t any reviews from people who’ve taken 50-milligram (mg) or 100-mg sildenafil tablets. However, you may experience mild or severe side effects from sildenafil with any prescribed dose.

In clinical trials,* a similar number of people reported certain side effects with both 50-mg and 100-mg doses. These side effects included mild to moderate headaches, flushing, and back pain. However, people taking the 100-mg dose had an increased risk of upset stomach, vision changes, and runny nose.

If you have questions about the side effects of your prescribed sildenafil dose, talk with your doctor or pharmacist.

* To learn more about the clinical trials of sildenafil, refer to the drug’s prescribing information for erectile dysfunction and pulmonary arterial hypertension (PAH).

Does sildenafil cause different side effects in females?

No, sildenafil isn’t known to cause different side effects in females.* Sildenafil is approved to treat PAH in most adults, including females.

If you’re female and concerned about side effects with sildenafil, talk with your doctor.

Note: If you’re male, priapism may occur during sildenafil treatment. With priapism, you experience a continued (4 hours or longer) erection that’s often painful. For more information about this side effect, see the “Sildenafil: Side effect specifics” section below.

* Sex and gender exist on spectrums. Use of the term “female” and “male” in this article refers to sex assigned at birth.

It’s possible to develop long-term side effects from sildenafil treatment. In clinical trials,* long-term side effects, such as vision loss and hearing loss,† occurred at any time during treatment. However, the exact reason why these side effects occurred is not fully known.

If you have any sudden changes in your vision or hearing, talk with your doctor right away. Also talk with them if you’re concerned about long-term side effects with sildenafil treatment.

* To learn more about the clinical trials of sildenafil, refer to the drug’s prescribing information for erectile dysfunction and pulmonary arterial hypertension.
† For more details about these side effects, including their symptoms, see the “Sildenafil: Serious side effects” section above.

Learn more about some of the side effects that sildenafil may cause. To find out how often side effects occurred in clinical trials, see the drug’s prescribing information for erectile dysfunction (ED) and pulmonary arterial hypertension (PAH).

Low blood pressure

Sildenafil may cause low blood pressure. However, this side effect was rare in clinical trials.* Sildenafil is a vasodilator, meaning it widens the blood vessels and makes it easier for blood to flow. When this happens, your blood pressure may drop. This is because your heart doesn’t have to work as hard to move blood around your body.

Signs and symptoms of low blood pressure include tiredness, lightheadedness, or blurry vision. They may also include nausea, dizziness, fainting, and confusion.

Low blood pressure can be mild or severe depending on how much your blood pressure drops. You may have an increased risk of severe low blood pressure if you:

What you can do

If you take blood pressure drugs during sildenafil treatment, your doctor will recommend monitoring your blood pressure regularly. If you notice any signs or symptoms of low blood pressure while taking sildenafil, talk with your doctor. They’ll review your symptoms and other medications to make sure it’s safe for you to keep taking the drug.

* To learn more about the clinical trials of sildenafil, refer to the drug’s prescribing information for ED and PAH.

Headache

Headache is a possible side effect while taking sildenafil. Headaches were common and typically mild in clinical trials of the drug.*

What you can do

If you start to experience headaches often or if they affect your daily life, talk with your doctor. They may recommend lifestyle changes, such as more rest to help ease your headache. Your doctor may also recommend pain medications to help treat your headache. These may include ibuprofen (Advil, Motrin) or acetaminophen (Tylenol).

* To learn more about the clinical trials of sildenafil, refer to the drug’s prescribing information for ED and PAH.

Cardiovascular problems

Severe cardiovascular problems may occur during sildenafil treatment. This side effect was reported* in people taking sildenafil for ED after the drug was approved. Cardiovascular problems, such as heart attack, stroke, irregular heartbeat, lung bleeding, and brain bleeding were rarely reported. Many of these reported side effects occurred during or shortly after sexual activity.

Symptoms can include:

  • fast heart rate
  • chest pain
  • trouble breathing
  • left shoulder or left arm pain
  • dizziness

Most of the people who experienced cardiovascular problems during sildenafil treatment already had other heart-related conditions. So it’s unknown if sildenafil was the direct cause of these side effects. They may be due to other factors, such as preexisting heart disease, sexual activity, or a combination of these factors.

What you can do

Before you start sildenafil treatment, be sure to tell your doctor if you have any heart conditions. Depending on your heart health, sildenafil may not be safe for you to take. Your doctor can review the risks and benefits of taking sildenafil to determine the right treatment plan for you.

If you’re interested in having sex while taking sildenafil for ED or PAH, talk with your doctor before starting treatment.

It’s important to talk with your doctor about your heart health before having sex. Engaging in sexual activity when you have heart problems may increase your risk of severe cardiovascular problems, including heart attack. This risk may increase further if you take sildenafil, have heart problems, and have sex. Your doctor can review the risks and benefits of having sex during sildenafil treatment.

* To learn more about the clinical trials of sildenafil, refer to the drug’s prescribing information for ED and PAH.

Nosebleeds

Nosebleeds are a common side effect of sildenafil, and they’re typically mild. In clinical trials,* people who were taking warfarin (Jantoven) had an increased risk of nosebleeds.

Symptoms of nosebleeds include bleeding from one or both nostrils. It also includes feeling as if you have to swallow a lot.

What you can do

If you start to experience nosebleeds often or if they don’t stop, talk with your doctor. They may recommend applying a cold cloth to the bridge of your nose briefly or pinching your nostrils for a short period of time. Your doctor may also recommend medications to help with nosebleeds, such as oxymetazoline (Afrin).

* To learn more about the clinical trials of sildenafil, refer to the drug’s prescribing information for ED and PAH.

Priapism

Priapism may occur during sildenafil treatment. With priapism, you experience a continued (4 hours or longer) erection that’s often painful. It usually happens without sexual stimulation or continues long after sex. Priapism was a rare side effect in clinical trials of sildenafil.*

Priapism can become a serious side effect if your erection lasts longer than 4 hours. If you’ve ever had sickle cell anemia, multiple myeloma, or leukemia, you may have an increased risk of developing severe priapism.

What you can do

Call 911 (or your local emergency number) and go to the emergency room if you experience an erection that lasts longer than 4 hours. You may experience permanent damage to your penis if this is not treated right away.

If your erections are lasting longer than usual, but less than 4 hours, talk with your doctor. They may recommend decreasing your sildenafil dosage.

* To learn more about the clinical trials of sildenafil, refer to the drug’s prescribing information for ED and PAH.

Allergic reaction

As with most drugs, sildenafil can cause an allergic reaction in some people. However, these reactions were rarely reported in clinical trials.*

Symptoms can be mild or serious and can include:

  • skin rash
  • itching
  • flushing
  • hives
  • low blood pressure
  • fainting
  • swelling under your skin, typically in your eyelids, lips, hands, or feet
  • swelling of your mouth, tongue, or throat, which can make it hard to breathe

What you can do

For mild symptoms of an allergic reaction, call your doctor right away. They may recommend ways to ease your symptoms and help determine whether you should keep taking sildenafil. However, if your symptoms are serious and you think you’re having a medical emergency, immediately call 911 or your local emergency number.

* To learn more about the clinical trials of sildenafil, refer to the drug’s prescribing information for ED and PAH.

Be sure to talk with your doctor about your health history before you take sildenafil. This drug may not be the right treatment for you if you have certain medical conditions or other factors that affect your health. These are considered drug-condition or drug-factor interactions. The conditions and factors to consider include:

Pulmonary vascular occlusive disease (PVOD). If you’ve ever had PVOD, taking sildenafil can lead to heart problems. Your doctor won’t typically recommend taking sildenafil if you’ve ever had PVOD. Talk with your doctor if you develop fluid in your lungs while taking sildenafil. This may be a sign of PVOD. If you develop PVOD, your doctor will likely recommend another medication for your condition.

Allergic reaction. If you’ve had an allergic reaction to sildenafil or any of its ingredients, your doctor will likely not prescribe sildenafil. Taking sildenafil could cause you to have another allergic reaction. Ask your doctor what other medications may be better options for you.

Certain eye disorders. Talk with your doctor if you’ve ever had eye disorders or if you start to experience vision loss while taking sildenafil. An eye condition called non-arteritic anterior ischemic optic neuropathy (NAION) may occur in people taking sildenafil.

Certain factors can increase your risk of developing NAION during sildenafil treatment. These include previous eye conditions or coronary artery disease. They also include being age 50 years or older or smoking. Before starting sildenafil treatment, be sure to tell your doctor if you have any of these factors. They’ll help determine if the drug is right for you.

Sickle cell anemia. If you have sickle cell anemia, tell your doctor. You may have an increased risk of vaso-occlusive crisis (VOC) if you have sickle cell anemia and take sildenafil. With VOC, your blood cells block blood flow to your organs, which can be painful. Be sure to talk with your doctor if you have sickle cell anemia. They’ll advise if sildenafil is right for you.

Conditions related to the shape of your penis. If you have conditions related to the shape of your penis, such as Peyronie’s disease, tell your doctor. These conditions may increase your risk of severe priapism* during sildenafil treatment. If you experience an erection lasting longer than 4 hours, call 911 or your local emergency number immediately.

If you take nitrates for any reason. Taking sildenafil with drugs containing nitrates is contraindicated. (A contraindication is a factor or condition that could prevent your doctor from prescribing a drug due to risk of harm.) This is due to sildenafil’s potential to cause severe low blood pressure.* Examples of nitrates include nitroglycerin (Nitrolingual), isosorbide (Isordil), nitroprusside (Nitropress). If you take any of these drugs or any other nitrates, be sure to tell your doctor before starting sildenafil treatment.

If you take guanylate cyclase (GC) stimulators. Sildenafil is contraindicated if you take a GC stimulator, including riociguat (Adempas). This is because these drugs may cause severe low blood pressure. Be sure to tell your doctor if you take this drug. They’ll likely recommend you do not take riociguat with sildenafil.

* For more details about this side effect, see the “Sildenafil: Serious side effects” section above.

Pregnancy and breastfeeding while taking sildenafil

It’s unknown whether sildenafil is safe to take while pregnant or breastfeeding.

Animal studies* did not show harm to the fetus when the drug was exposed to pregnant animals. However, keep in mind that animal studies don’t always reflect what will happen in humans.

If you’re pregnant or can become pregnant, talk with your doctor. They’ll review the risks and benefits with you and advise whether sildenafil treatment is right for you. In certain cases, your doctor may recommend that you continue taking sildenafil during pregnancy.

Sildenafil may pass into breast milk, but it isn’t known how this could affect a child who is breastfed. If you are breastfeeding or planning to breastfeed, talk with your doctor. They can review the risks and benefits of taking sildenafil while breastfeeding.

* To learn more about these studies, refer to the drug’s prescribing information for ED and PAH.

If you are taking sildenafil for erectile dysfunction or pulmonary arterial hypertension, it’s possible to experience side effects. Most side effects are mild to moderate in severity. If you’re experiencing symptoms of severe side effects while taking sildenafil, talk with your doctor right away.

If you’d like to learn more about sildenafil, talk with your doctor or pharmacist. They can help answer any questions you have about side effects from taking the drug.

A generic drug and its brand-name version contain the same active ingredient, so they’re expected to have the same side effects. Referring to the following articles about sildenafil and Viagra can provide you with additional information:

  • More information about sildenafil. For details about other aspects of sildenafil, refer to this article.
  • Drug comparison. To learn how sildenafil compares with Viagra, read this article.
  • Cost. If you’d like to learn about sildenafil and cost, see this article.
  • A look at your condition. For details about your condition, see our hypertension hub. You can also view our men’s health hub and this list of erectile dysfunction and premature ejaculation articles.

Disclaimer: Medical News Today 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 another healthcare professional before taking any medication. The drug information contained herein 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.