If you have certain health conditions or are taking certain medications, your doctor may tell you to take tadalafil less often or may prescribe a lower dose to be taken once a day. One of the first Cialis ads aired at the Super Bowl. Taking tadalafil alone is not enough to cause an erection. Effects may last up to 36 hours. A dose of Cialis can remain effective in the body for up to 36 hours. Your doctor will help you decide the best time for you to take tadalafil before sexual activity. Take tadalafil exactly as directed.Tadalafil (Cialis) is used to treat erectile dysfunction (ED, impotence; inability to get or keep an erection), and the symptoms of benign prostatic hyperplasia (BPH; an enlarged prostate) which include difficulty urinating (hesitation, dribbling, weak stream, and incomplete bladder emptying), painful urination, and urinary frequency and urgency in adult men. 5 mg 10 mg 20 mg The cost for these different strengths depends on whether you have insurance, your individual plan coverage, and your treatment plan. For example, Cialis . 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 .