These include a heart attack, stroke or a serious heart rhythm disorder in the past six months. It lasts 4 to 5 hours, or longer if you have mild to moderate ED. Avanafil Stendra. Take sildenafil exactly as directed. As with sildenafil, a high-fat meal or alcohol keep the body from absorbing it as quickly.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 . Do not take VIAGRA if you: take any medicines called nitrates, often prescribed for chest pain, or guanylate cyclase stimulators like Adempas (riociguat) for pulmonary . Drug Images What is Viagra? If you have erectile dysfunction (ED), your doctor may recommend that you take Viagra. It’s a prescription drug that’s used in adult males* .