It may be taken with or without food. Talk to your doctor about eating grapefruit and drinking grapefruit juice while taking this medicine. 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. Keep from freezing. This medicine is also used to treat erectile dysfunction and signs and symptoms of BPH. · Adults—10 milligrams (mg) as a single dose, no more than once a day, taken 30 minutes before you think sexual activity may occur. Your doctor may adjust your dose . 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 . Cialis is a prescription medication containing the active ingredient tadalafil. Cialis belongs to a group of medications known as phosphodiesterase-5 (PDE-5) .