It works for up to 36 hours. Sildenafil Viagra. How oral medicines differ Each oral medicine for ED has a slightly different chemical makeup. Its effects might last longer if you have mild to moderate ED. This medication is taken with or without food an hour before sex. When choosing one, tell your doctor or other health care professional what your preferences are, such as cost, ease of use, how long the drug’s effects last and side effects.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 . Last updated: June 14, If you’re looking for a less costly Viagra, you might want to ask your doctor about sildenafil. It’s the active ingredient in both branded Viagra and the drug. Save. As Shelley says, you won’t be able to get inhalers without a prescription. And Bahamian pharmacies do not accept US prescriptions, so you would need to visit a .