A newer form of the medicine that dissolves on the tongue might work faster than the pill that you swallow. How oral medicines differ Each oral medicine for ED has a slightly different chemical makeup. They’re often the first line of treatment for trouble getting or keeping an erection, called erectile dysfunction ED. Too much can cause a priapism, an uncomfortable and disproportionately large erection that lasts for more than four hours. Sildenafil Viagra. An inherited eye disease that affects the retina.Oral medicines for ED usually work well and cause few side effects. The four main medicines taken by mouth for erectile dysfunction are: Avanafil (Stendra). Sildenafil . Medically reviewed by Melissa Badowski, PharmD, MPH, FCCP — By Jennifer Mitri Williamson, Pharm.D. — Updated on September 12, Learn about .