In this case, just leave out the missed dose and take your next dose at the usual time. Follow your doctor’s orders or the directions on the label. Keep from freezing. The four main medicines taken by mouth for erectile dysfunction are: Avanafil Stendra. For treatment of erectile dysfunction: For oral dosage form tablets : Adults up to 65 years of age—50 milligrams mg as a single dose no more than once a day, 1 hour before sexual intercourse. Use only the brand of this medicine that your doctor prescribed.For professionals 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 . FAQ What is Viagra? Viagra relaxes muscles found in the walls of blood vessels and increases blood flow to particular areas of the body. Viagra is used to treat erectile . 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 .