It lasts 4 to 5 hours, or longer if you have mild to moderate ED. The four main medicines taken by mouth for erectile dysfunction are: Avanafil Stendra. Rarely reported side effects include: an erection that will not go away priapism. How oral medicines differ Each oral medicine for ED has a slightly different chemical makeup. It might work longer if you have mild to moderate erectile dysfunction.Sildenafil (Viagra). This medicine works best when you take it on an empty stomach an hour before sex. The body takes longer to absorb it after a high-fat meal or alcohol. Its effects . Viagra (sildenafil) is a brand-name oral tablet prescribed for erectile dysfunction. The cost of the drug with and without insurance can depend on several factors, such as whether . Drug Images What is Viagra? 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. .