By controlling the enzyme, tadalafil helps to maintain an erection after the penis is stroked by increasing blood flow to the penis. Our expert reviewers devote hours to testing and comparing products so that you can make informed decisions about the best options for you. This is because the shelf life is determined by several variables, including the manufacturer, pharmacy, and storage parameters. Tadalafil works on the PDE5 enzyme in the lungs to relax the blood vessels. Taking Cialis does not mean you are guaranteed to get an erection.Cialis (tadalafil) is an orally administered prescription medication used for erectile dysfunction (ED) and pulmonary arterial hypertension (PAH) to reduce the . · Cialis is a prescription drug used to treat erectile dysfunction and benign prostatic hyperplasia. Learn about its dosages, form, strengths, and more. 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 .