Tadalafil does not prevent pregnancy or the spread of sexually transmitted diseases such as human immunodeficiency virus HIV. Other conditions that may disqualify you from an ED prescription include a history of stroke, kidney or liver disease, cancer, diabetes, or a bleeding disorder. An erection results from an increase in blood flow to the penis. Persons surnamed “Cialis” objected to Eli Lilly and Company’s so naming the drug, but the company has maintained that the drug’s trade name is unrelated to the surname. Take tadalafil exactly as directed.Side Effects. Headache, stomach upset, back pain, muscle pain, stuffy nose, flushing, or dizziness may occur. If any of these effects last or get worse, tell your doctor or pharmacist promptly. To. Learn more about Cialis oral. 1. This is a generic drug. The average cost for 30 Tablet(s), 5mg each of the generic (tadalafil) is $ You can buy tadalafil at the discounted price of $ by using the MDRx coupon, a savings of 93%. Even if this drug is covered by Medicare or your insurance, we recommend you compare prices. How Cialis Works. Tadalafil and other PDE5 inhibitors primarily work by inducing muscle relaxation. Tadalafil stops the breakdown of a chemical responsible for relaxing muscles. In ED and PAH, the drug targets muscle cells in blood vessels. When the blood vessel muscle cells relax, this expands the vessel and increases blood flow; this .