When the blood vessel muscle cells relax, this expands the vessel and increases blood flow; this effect is referred to as vasodilation. Tadalafil is also sometimes taken once a day every day without regard to timing of sexual activity. Cialis is also highly effective in reducing the symptoms of BPH. John’s wort. If you are taking tadalafil to treat erectile dysfunction, follow your doctor’s directions and the guidelines in this paragraph. Tadalafil may cause side effects.Cialis (tadalafil) is an orally administered prescription medication used for erectile dysfunction (ED) and pulmonary arterial hypertension (PAH) to reduce . Tadalafil (Cialis) is a phosphodiesterase-5 enzyme (PDE-5) inhibitor. It works by blocking PDE This is a protein in your body that breaks down the molecules that .  · Tadalafil is used to treat men who have erectile dysfunction (also called sexual impotence). Tadalafil belongs to a group of medicines called phosphodiesterase .