What Is Cialis? Medicines that block an enzyme called CYP3A4. Summary Cialis and Viagra are both pills for treating erectile dysfunction. Take tadalafil exactly as directed. We rely on peer-reviewed studies, academic research institutions, and medical associations. One of these is PAH.tadalafil or cialis Savings, Coupons and Information. | TADALAFIL (tah DA la fil) treats erectile dysfunction (ED). It works by increasing blood flow to the penis, which helps to maintain an erection. Generic Viagra (sildenafil) is available as a , , , and milligram (mg) pill and in liquid form. It’s meant to be taken as needed — about an hour before sex — but shouldn’t be. Generic Cialis, or Tadalafil, is available in several doses in tablet form: milligrams (mg), 5 mg, 10 mg, and 20 mg. Depending on the dose for ED, you can use it as needed before sexual.