The four main medicines taken by mouth for erectile dysfunction are: Avanafil Stendra. How oral medicines differ Each oral medicine for ED has a slightly different chemical makeup. Oral ED medicines might not work or might be dangerous if you also take any of the following: Nitrate medicines. This boosts blood flow and helps you get an erection from sexual activity. They enhance the effects of a chemical the body makes that relaxes muscles in the penis, called nitric oxide. Side effects Side effects of oral ED medicines are often mild.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 . Don’t be fooled into buying “herbal viagra.” Never take any medicines that claim to be the “herbal” or nonprescription version of an oral medicine for ED. These . Drug Facts Common Brands Viagra Drug Class PDE-5 inhibitor Controlled Substance Classification Not a controlled medication Generic Status Lower-cost generic .