Treating erectile dysfunction (ED). It may also be used for other conditions as determined by your doctor.

Viagra is a phosphodiesterase inhibitor. It works by helping to increase blood flow into the penis during sexual stimulation. This helps you to achieve and maintain an erection.

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, butyl nitrate)

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

Before using Viagra :

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, Peyronie disease, cavernosal fibrosis), blood problems (eg, sickle cell anemia, leukemia, multiple myeloma), or any other condition that may increase the risk of a prolonged erection (eg, priapism)
* if you have a history of certain eye problems (eg, retinitis pigmentosa, sudden vision loss, optic neuropathy, macular degeneration)
* if you have a history of liver or kidney problems, high or low blood pressure, ulcers, bleeding problems, heart problems (eg, heart failure, irregular heartbeat, aortic stenosis, angina), 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), amlodipine, 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), cimetidine, H2 agonists (eg, famotidine), HIV protease inhibitors (eg, ritonavir), macrolide antibiotics (eg, erythromycin), 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.