What is Viagra? Viagra is a brand-name prescription drug that’s approved to treat erectile dysfunction (ED). With ED, you’re unable to have or maintain an erection. Viagra is .You can take sildenafil with or without food. Sildenafil Viagra. Also tell your doctor if you have or have ever had pulmonary veno-occlusive disease PVOD; blockage of veins in the lungs ; a stomach ulcer; heart, kidney, or liver disease; a heart attack; heart failure; angina chest pain ; an irregular heartbeat; a stroke; chest pain; high or low blood pressure; high cholesterol; a bleeding disorder; blood circulation problems; blood cell problems such as sickle cell anemia a disease of the red blood cells , multiple myeloma cancer of the plasma cells , or leukemia cancer of the white blood cells ; conditions affecting the shape of the penis e. The following nonprescription or herbal products may interact with sildenafil: cimetidine Tagamet HB , St. Tell your doctor or pharmacist if you are taking nitrates medications for chest pain such as isosorbide dinitrate Isordil , isosorbide mononitrate Monoket , and nitroglycerin Nitromist, Nitro-Dur, Nitrostat.It’s a prescription drug that’s used in adult males* with ED. With ED, you have trouble getting or keeping an erection. To find out more about how Viagra is used for ED, see the “ . Sildenafil is in a class of medications called phosphodiesterase (PDE) inhibitors. Sildenafil treats erectile dysfunction by increasing blood flow to the penis during sexual stimulation. . Viagra (sildenafil) is a prescription drug that’s used to treat erectile dysfunction (ED). The drug comes as a tablet you’ll take by swallowing. It’s usually taken as needed about 1 .What special dietary instructions should I follow? 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. The following nonprescription or herbal products may interact with sildenafil: cimetidine Tagamet HB , St. Tell your doctor if sildenafil is not working well or if you are experiencing side effects. When oral medications might not be safe Check with your health care team before you take any medicine for erectile dysfunction. If you ever need emergency medical treatment for a heart problem, the healthcare providers who treat you will need to know when you last took sildenafil. Be sure to let your doctor and pharmacist know that you are taking these medications before you start taking sildenafil.