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. What side effects can this medication cause? When oral medications might not be safe Check with your health care team before you take any medicine for erectile dysfunction. Take sildenafil at around the same times every day. If you become pregnant while taking sildenafil, call your doctor. The four main medicines taken by mouth for erectile dysfunction are: Avanafil Stendra.Ask your doctor. Q&A. Drug Images. What is Viagra? If you have erectile dysfunction (ED), your doctor may recommend that you take Viagra. It’s a prescription drug that’s used in . Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. They enhance the effects of a chemical the body makes that relaxes muscles . Viagra (sildenafil) is a prescription drug that’s used to treat erectile dysfunction (ED). The drug comes as a tablet you’ll take by swallowing. It’s usually taken as needed about 1 .