Do NOT use Viagra if:

• you are allergic to any ingredient in Viagra
• you have been advised by your doctor to avoid sexual activity because of heart problems
• you are taking nitrates (eg, isosorbide, nitroglycerin) in any form (eg, tablet, capsule, patch, ointment), or nitroprusside
• you use certain recreational drugs called "poppers" (eg, amyl nitrate or nitrite, butyl nitrate or nitrite)
• you take another PDE5 inhibitor (eg, tadalafil, vardenafil) or another medicine that contains sildenafil.

Contact your doctor or health care provider right away if any of these apply to you.

Some medical conditions may interact with Viagra. Tell your doctor or pharmacist if you have any medical conditions, especially if any of the following apply to you:

• if you are taking any prescription or nonprescription medicine, herbal preparation, or dietary supplement
• if you have allergies to medicines, foods, or other substances
• if you have a deformed penis (eg, cavernosal fibrosis, Peyronie disease), blood cell problems (eg, leukemia, multiple myeloma, sickle cell anemia), or any other condition that may increase the risk of a prolonged erection (priapism)
• if you have a history of a prolonged (more than 4 hours) or painful erection (priapism)
• if you have a history of certain eye problems (eg, macular degeneration, optic neuropathy, retinitis pigmentosa, sudden vision loss in one or both eyes) or hearing problems (eg, ringing in the ears, decreased hearing, hearing loss)
• if you have a history of liver or kidney problems, lung problems (eg, pulmonary veno-occlusive disease), high or low blood pressure, ulcers, bleeding problems, heart problems (eg, angina, aortic stenosis, heart failure, irregular heartbeat), or blood vessel problems
• if you have a history of heart attack, stroke, or life-threatening irregular heartbeat, especially within the past 6 months.

Some medicines may interact with Viagra. Tell your health care provider if you are taking any other medicines, especially any of the following:

• Alpha-blockers (eg, doxazosin), medicines for high blood pressure, nitrates (eg, isosorbide, nitroglycerin), or nitroprusside because severe low blood pressure with dizziness, lightheadedness, and fainting may occur
• Azole antifungals (eg, itraconazole, ketoconazole), H₂ antagonists (eg, cimetidine), HIV protease inhibitors (eg, ritonavir, saquinavir), macrolide antibiotics (eg, erythromycin), narcotic analgesics (eg, dihydrocodeine), or telithromycin because they may increase the risk of Viagra's side effects
• Bosentan or rifampin because they may decrease Viagra's effectiveness.

This may not be a complete list of all interactions that may occur. Ask your health care provider if Viagra may interact with other medicines that you take. Check with your health care provider before you start, stop, or change the dose of any medicine.

Important safety information:

• Viagra may cause dizziness, drowsiness, fainting, or blurred vision. These effects may be worse if you take it with alcohol or certain medicines. Use Viagra with caution. Do not drive or perform other possible unsafe tasks until you know how you react to it.
• Viagra may cause dizziness, lightheadedness, or fainting; alcohol, hot weather, exercise, or fever may increase these effects. To prevent them, sit up or stand slowly, especially in the morning. Sit or lie down at the first sign of any of these effects.
• Patients with heart problems who take Viagra may be at increased risk for heart-related side effects, including heart attack or stroke. Symptoms of a heart attack may include chest, shoulder, neck, or jaw pain; numbness of an arm or leg; severe dizziness, headache, nausea, stomach pain, or vomiting; fainting; or vision changes. Symptoms of a stroke may include confusion, vision or speech changes, one-sided weakness, or fainting. Contact your doctor or seek medical attention right away if you experience these symptoms.
• Viagra may rarely cause a prolonged (eg, more than 4 hours) or painful erection. This could happen even when you are not having sex. If this is not treated right away, it could lead to permanent sexual problems such as impotence. Contact your doctor right away if you have an erection that lasts more than 4 hours.
• Viagra does not stop the spread of HIV or other sexually transmitted diseases (STDs) to others through sexual contact. Use barrier methods of birth control (eg, condoms) if you have HIV infection or an STD.
• Viagra will not prevent pregnancy. If your partner may become pregnant and you wish to avoid pregnancy, be sure to use an effective form of birth control.
• Viagra may uncommonly cause mild, temporary vision changes (eg, blurred vision, sensitivity to light, blue/green color tint to vision). Contact your doctor if vision changes persist or are severe.
• Rarely, an eye problem called nonarteritic anterior ischemic optic neuropathy (NAION) has been reported in patients who took Viagra. This may lead to decreased vision or permanent loss of vision in some cases. If you notice a sudden decrease in vision or loss of vision in one or both eyes, contact your doctor right away.
• Sudden decreases in hearing and loss of hearing have been reported in some patients who have taken Viagra. Sometimes they also noticed ringing in the ears or dizziness. If you notice a sudden decrease or loss of hearing, contact your doctor right away.
• Do not use other medicines or treatments for ED while you are taking Viagra without first checking with your doctor.
• Use Viagra with caution in the elderly; they may be more sensitive to its effects.
• Viagra is not recommended for use in children younger than 18 years old.

All medicines may cause side effects, but many people have no, or minor, side effects.

Check with your doctor if any of these most common side effects persist or become bothersome:

Diarrhea; dizziness; flushing; headache; heartburn; stuffy nose; upset stomach.

Seek medical attention right away if any of these severe side effects occur:

Severe allergic reactions (rash; hives; itching; difficulty breathing; tightness in the chest; swelling of the mouth, face, lips, or tongue); chest pain; fainting; fast or irregular heartbeat; memory loss; numbness of an arm or leg; one-sided weakness; painful or prolonged erection; ringing in the ears; seizure; severe or persistent dizziness; severe or persistent vision changes; sudden decrease or loss of hearing; sudden decrease or loss of vision in one or both eyes.

This is not a complete list of all side effects that may occur. If you have questions about side effects, contact your health care provider.