Tell your doctor if tadalafil is not working well or if you are experiencing side effects. ED occurs more frequently in older men. Talk to your doctor about eating grapefruit and drinking grapefruit juice while taking this medicine. If you ever need emergency medical treatment for a heart problem, the health care providers who treat you will need to know when you last took tadalafil. What special dietary instructions should I follow?Tadalafil (Cialis) is a phosphodiesterase-5 enzyme (PDE-5) inhibitor. It works by blocking PDE This is a protein in your body that breaks down the molecules that . Published on October 18, warning This article is no longer being updated and some information may not be current. Visit the GoodRx Healthhomepage for our latest articles. . Cialis comes in several strengths: milligrams (mg), 5mg, 10 mg, and 20 mg. The Cialis cost per pill and daily cost depend on several factors, such as: the strength prescribed by your doctor.