It lasts 4 to 5 hours, or longer if you have mild to moderate ED. These medicines all work well for ED. These include a heart attack, stroke or a serious heart rhythm disorder in the past six months. Generic versions of sildenafil, vardenafil and tadalafil are available. Patients should always ask their doctors for medical advice about adverse events. · Take sildenafil exactly as it was prescribed for you. Follow all directions on your prescription label and read all medication guides or instruction sheets. Revatio is . Your prescription may have been filled with a generic version instead of brand-name VIAGRA. Follow the steps below to help ensure you receive the brand name your doctor . Drug Facts Common Brands Viagra Drug Class PDE-5 inhibitor Controlled Substance Classification Not a controlled medication Generic Status Lower-cost generic .