Without physical action to the penis, such as that occurring during sexual intercourse, tadalafil will not work to cause an erection. Do not double doses. Tadalafil is also sometimes taken once a day every day without regard to timing of sexual activity. Liver function: Liver disease or reduced liver function may cause Cialis Tadalafil to build up in the body, causing side effects. What special precautions should I follow?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.  · Cialis; Descriptions. Tadalafil is used to treat men who have erectile dysfunction (also called sexual impotence). Tadalafil belongs to a group of medicines called phosphodiesterase 5 (PDE5) inhibitors. These medicines prevent an enzyme called phosphodiesterase type-5 from working too quickly. The penis is one of the areas where .  · For treatment of benign prostatic hyperplasia (daily use): Adults—5 milligrams (mg) as a single dose, no more than once a day, taken at the same time each day. Children—Use is not recommended. For treatment of erectile dysfunction (as needed): Adults—10 milligrams (mg) as a single dose, no more than once a day, taken 30 minutes .