You should only be treated with one of these products at a time. They have the same benefits and risks as their brand-name counterparts. Finding an online ED provider can feel overwhelming. By controlling the enzyme, sildenafil helps to maintain an erection after the penis is stroked. If you experience chest pain, dizziness, or nausea during sex, seek immediate medical help.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 hour. Generic Viagra (sildenafil) is available as a , , , and milligram (mg) pill and in liquid form. It’s meant to be taken as needed — about an hour before sex — but shouldn’t be. VIAGRA can cause your blood pressure to drop suddenly to an unsafe level if taken with certain other medicines. Do not take VIAGRA if you take any other medicines called “nitrates.” Nitrates are used to treat chest pain (angina). A sudden drop in blood pressure can cause you to feel dizzy, faint, or have a heart attack or stroke.