These medicines all work well for ED. Severe liver disease. It works for up to 36 hours. The four main medicines taken by mouth for erectile dysfunction are: Avanafil Stendra. When a man is sexually stimulated, his body’s normal response is to increase blood flow to his penis to produce an erection. When oral medications might not be safe Check with your health care team before you take any medicine for erectile dysfunction.Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. They enhance the effects of a chemical the body makes that relaxes muscles in the penis, called nitric oxide. This boosts blood flow and helps you get an erection from sexual activity. Sildenafil (Viagra) is used to treat erectile dysfunction (impotence; inability to get or keep an erection) in men. Sildenafil (Liqrev, Revatio) is used to improve the ability to exercise in adults (Liqrev, Revatio) and children 1 year of age and older (Revatio) with pulmonary arterial hypertension (PAH; high blood pressure in the vessels. 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 approved for this use in males.