Tell your doctor if any of these symptoms are severe or do not go away: headache. With PAH, high blood pressure develops when a blockage in the arteries within the lung limits normal blood flow. There are two different ways to take tadalafil, either daily or on an as needed basis. Mechanism of action[ edit ] Penile erection during sexual stimulation is caused by increased penile blood flow resulting from the relaxation of penile arteries and the smooth muscle of the corpus cavernosum. If your dose is different, do not change it unless your doctor tells you to do so.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 .  · Adults—5 milligrams (mg) once a day, taken at the same time each day, without regard for the timing of sexual activity. Children—Use is not recommended. For .  · Cialis (tadalafil) is prescribed to treat erectile dysfunction and symptoms of benign prostatic hyperplasia. It comes as a tablet that’s taken as needed or once per .