Stop taking VIAGRA and call your healthcare provider right away if you have any sudden vision loss sudden hearing decrease or hearing loss. An inherited eye disease that affects the retina. Recent heart or blood vessel problems. These medicines all work well for ED. Severe liver disease. This medicine also works best when you take it an hour before sex on an empty stomach. How oral medicines differ Each oral medicine for ED has a slightly different chemical makeup.generic Revatio and Viagra Used for Pulmonary Hypertension and Erectile Dysfunction MORE expand_more Check your prescription Prescription 20mg sildenafil (30 tablets) . Learn More IF YOU CHOOSE BRAND-NAME VIAGRA, MAKE SURE YOU GET THE BRAND NAME Your prescription may have been filled with a generic version instead of . Drug Facts Common Brands Viagra Drug Class PDE-5 inhibitor Controlled Substance Classification Not a controlled medication Generic Status Lower-cost generic available .