Tadalafil treats PAH by relaxing the blood vessels in the lungs to allow blood to flow more easily. Sildenafil Viagra. For CIALIS for use as needed, over and subjects were treated for at least 6 months and 1 year, respectively. These include a heart attack, stroke or a serious heart rhythm disorder in the past six months. In such circumstances, nitrates should still only be administered under close medical supervision with appropriate hemodynamic monitoring. B No evidence of risk in humans Based on FDA pregnancy categories Do not start or stop taking tadalafil during pregnancy without your doctor’s advice. · The approved dosages of Cialis for ED, BPH symptoms, or both, are between mg and 20 mg a day or as needed. Dosages higher than 20 mg a day haven’t been studied, and it’s not known what. How Cialis Works. Tadalafil and other PDE5 inhibitors primarily work by inducing muscle relaxation. Tadalafil stops the breakdown of a chemical responsible for relaxing muscles. In ED and PAH, the drug targets muscle cells in blood vessels. When the blood vessel muscle cells relax, this expands the vessel and increases blood flow; this .  · Descriptions. Tadalafil is used to treat men who have erectile dysfunction (also called sexual impotence). Tadalafil belongs to a group of medicines called .