The mechanism of action for ED pills is simple: They inhibit the PDE5 enzyme which regulates the signals responsible for the smooth muscle tissue. You should take tadalafil one time a day. Tadalafil is also used in both men and women to treat the symptoms of pulmonary arterial hypertension to improve your ability to exercise. Ask your pharmacist for a list of the ingredients. Popular ED medications found online include: Viagra sildenafil : As the first FDA-approved PDE5 inhibitor for ED, sildenafil is taken 30 minutes to four hours before sexual intercourse to help achieve and maintain an erection. What Is Cialis?Cialis (tadalafil) is a moderately priced drug used to treat erection problems in men. It may also be used to treat the enlargement of the prostate gland. This drug is slightly more popular than comparable drugs. It is available in both brand and generic versions. 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 . Cialis (tadalafil) is a brand-name prescription medication. The Food and Drug Administration (FDA) has approved it for use in adult males.* It’s approved to.