Sildenafil relaxes muscles of the blood vessels and increases blood flow to particular areas of the body.

Sildenafil under the name Viagra is used to treat erectile dysfunction (impotence) in men.

Another brand of sildenafil is Revatio, which is used to treat pulmonary arterial hypertension and improve exercise capacity in men and women.

Do not take Viagra while also taking Revatio.

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 comes as a tablet and suspension (liquid) to take by mouth.

If you are taking sildenafil to treat erectile dysfunction, follow your doctor's directions and the guidelines in this paragraph. Take sildenafil as needed before sexual activity. The best time to take sildenafil is about 1 hour before sexual activity, but you can take the medication any time from 4 hours to 30 minutes before sexual activity. Sildenafil usually should not be taken more than once every 24 hours. If you have certain health conditions or are taking certain medications, your doctor may tell you to take sildenafil less often. You can take sildenafil with or without food. However, if you take sildenafil with a high-fat meal, it will take longer for the medication to start to work.

If you are taking sildenafil to treat PAH, you will probably take sildenafil three times a day with or without food. Take sildenafil at around the same times every day.

Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take sildenafil exactly as directed. Do not take more or less of it or take it more often than prescribed by your doctor.

Shake the liquid well for 10 seconds before each use to mix the medication evenly. Use the oral syringe provided with your medication to measure and take your dose. Follow the manufacturer's directions to use and clean the oral syringe. Do not mix the liquid with other medications or add anything to flavor the medication.

If you are taking sildenafil for erectile dysfunction, your doctor will probably start you on an average dose of sildenafil and increase or decrease your dose depending on your response to the medication. Tell your doctor if sildenafil is not working well or if you are experiencing side effects.

If you are taking sildenafil for PAH, you should know that sildenafil controls PAH but does not cure it. Continue to take sildenafil even if you feel well. Do not stop taking sildenafil without talking to your doctor.

Ask your pharmacist or doctor for a copy of the manufacturer's information for the patient.

Take sildenafil exactly as it was prescribed for you. Follow all directions on your prescription label and read all medication guides or instruction sheets.

Revatio is usually taken three times each day, about 4 to 6 hours apart.

Viagra is usually taken only when needed, 30 minutes to 1 hour before sexual activity. You may take it up to 4 hours before sexual activity. Do not take Viagra more than once per day.

Shake the oral suspension (liquid) before you measure a dose. Use the dosing syringe provided, or use a medicine dose-measuring device (not a kitchen spoon).

Viagra can help you have an erection when sexual stimulation occurs. An erection will not occur just by taking a pill. Follow your doctor's instructions.

During sexual activity, if you become dizzy or nauseated, or have pain, numbness, or tingling in your chest, arms, neck, or jaw, stop and call your doctor right away. You could be having a serious side effect of sildenafil.

Store at room temperature away from moisture and heat.

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).

Do not take this medicine 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); or

• if you have been told you should not have sexual intercourse for health reasons.

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 smoked or were over 50 years old. It is not clear whether this medicine is the actual cause of vision loss.

This medicine is not expected to harm an unborn baby. Tell your doctor if you are pregnant or plan to become pregnant. Women with pulmonary arterial hypertension should not stop taking sildenafil without talking to their doctor.

It is not known whether sildenafil passes into breast milk or if it could harm a nursing baby. Tell your doctor if you are breast-feeding a baby. Women with pulmonary arterial hypertension should not stop taking sildenafil without talking to their doctor.

Do not give this medication to anyone under 18 years old without medical advice.

Since Viagra is used as needed, you are not likely to miss a dose.

If you miss a dose of Revatio, take the medicine as soon as you can, but skip the missed dose if it is almost time for your next dose. Do not take two doses at one time.

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

Keep this medication in the container it came in, tightly closed, and out of reach of children. Store the tablets at room temperature and away from excess heat and moisture (not in the bathroom). Store the suspension at room temperature or in a refrigerator, but do not freeze it. Dispose of any unused suspension after 60 days.

It is important to keep all medication out of sight and reach of children as many containers (such as weekly pill minders and those for eye drops, creams, patches, and inhalers) are not child-resistant and young children can open them easily. To protect young children from poisoning, always lock safety caps and immediately place the medication in a safe location – one that is up and away and out of their sight and reach. http://www.upandaway.org

Unneeded medications should be disposed of in special ways to ensure that pets, children, and other people cannot consume them. However, you should not flush this medication down the toilet. Instead, the best way to dispose of your medication is through a medicine take-back program. Talk to your pharmacist or contact your local garbage/recycling department to learn about take-back programs in your community. See the FDA's Safe Disposal of Medicines website (http://goo.gl/c4Rm4p) for more information if you do not have access to a take-back program.

Talk to your doctor about eating grapefruit and drinking grapefruit juice while taking this medicine.

Drinking alcohol with sildenafil can cause side effects.

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.

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); or
• 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); or
• 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.

Do not take sildenafil with similar medications such as avanafil (Stendra), tadalafil (Cialis) or vardenafil (Levitra). Tell your doctor about all other medications you use for erectile dysfunction.

Do not take sildenafil if you take other medicines to treat pulmonary arterial hypertension, such as riociguat (Adempas).

Do not take sildenafil 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.

In addition, tell your doctor about all your other medicines, especially:

• drugs to treat high blood pressure or a prostate disorder;

• antifungal medicine - ketoconazole or itraconazole; or

• medicine to treat HIV/AIDS - ritonavir and others.

This list is not complete. Other drugs may interact with sildenafil, including prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible drug interactions are listed here.

Keep all appointments with your doctor.

Do not let anyone else take your medication. Ask your pharmacist any questions you have about refilling your prescription.

It is important for you to keep a written list of all of the prescription and nonprescription (over-the-counter) medicines you are taking, as well as any products such as vitamins, minerals, or other dietary supplements. You should bring this list with you each time you visit a doctor or if you are admitted to a hospital. It is also important information to carry with you in case of emergencies.