Do not double doses. What does this mean? Because it may last this long, Cialis should not be taken more than once daily. They enhance the effects of a chemical the body makes that relaxes muscles in the penis, called nitric oxide. This includes prescription or nonprescription over-the-counter [OTC] medicines and herbal or vitamin supplements. Take all of the tablets for your daily dose at one time each day; do not divide the tablets to take as separate doses. This is not a complete list of interactions; others may occur with Cialis. · Drug Images. What is Cialis? Cialis is a brand-name prescription medication. It’s FDA-approved to treat the following in males:* erectile dysfunction (ED), a condition in which you can’t get or. Tadalafil (Cialis) is available both as brand-name and generic tablets. Common side effects of this medication include headache and indigestion. Tadalafil (Cialis) does interact with some medications, such as heart and blood pressure medications, and taking them together could lead to very low blood pressure and dizziness. stockcam / Getty Images. What is generic Cialis? Generic Cialis is called tadalafil, which is the active ingredient in Cialis. Cialis is Food and Drug Administration (FDA) approved to treat.