Ask your doctor about any risk. Having pulmonary arterial hypertension PAH during pregnancy may cause heart failure, stroke, or other medical problems in both mother and baby. When the blood vessel muscle cells relax, this expands the vessel and increases blood flow; this effect is referred to as vasodilation. In BPH, the medication relaxes the urinary tract and bladder muscles, allowing for more effortless urine flow. Tadalafil works for these conditions by promoting muscle relaxation, which improves blood flow in PAH and urinary flow in BPH. With PAH, high blood pressure develops when a blockage in the arteries within the lung limits normal blood flow.Cialis is a prescription medication containing the active ingredient tadalafil. Cialis belongs to a group of medications known as phosphodiesterase-5 (PDE-5) inhibitors. Healthcare providers commonly prescribe tadalafil to treat erectile dysfunction (ED). Last updated on Uses Warnings Before taking Dosage Side effects Interactions FAQ What is Cialis? Cialis relaxes muscles of the blood vessels and increases blood flow to particular areas of the body. Cialis is used to treat erectile dysfunction (impotence) and symptoms of benign prostatic hypertrophy (enlarged prostate).  · Is taking Cialis 40 mg daily safe? Medically reviewed by Last updated on April 5, Official answer by The recommended daily dosage of Cialis is 20mg. By taking a high dose you increase the risks of severe side effects. .