Ask your pharmacist or doctor for a copy of the manufacturer’s information for the patient. In , Pfizer scientists discovered that sildenafil, which also inhibits the PDE5 enzyme, caused penile erection in males participating in a clinical study of a heart medicine. Understanding Erectile Dysfunction and Its Treatment Cialis, scientifically known as Tadalafil, is a prescription medication primarily used to treat erectile dysfunction ED in men. Comparison with actions of other PDE5 inhibitors[ edit ] Sildenafil and vardenafil inhibit PDE6, an enzyme found in the eye, more than tadalafil. Cialis has a longer duration of action, up to 36 hours, compared to other ED medications.Cialis (tadalafil) is a popular medication used to treat erectile dysfunction. It’s available in tablets ranging from mg to 20mg. It can cost more than $ for a month’s supply, depending on the dosage you need and the pharmacy you visit. You can save more than 90% on the average retail price at certain pharmacies by using a GoodRx coupon.  · The typical dose for once-daily Cialis for ED is milligrams (mg) to 5 mg. When used as needed for ED, the usual Cialis dose is 10 mg (with a maximum daily dose of 20 mg). The typical dose of. TADALAFIL (Generic for CIALIS) QTY 30 • 5 MG • Tablet • Near Add to Medicine Chest Set Price Alert Form Dosage Location Near Pricing Drug Information Drug .