You can take it in a small dose daily or in a larger dose as needed. Click here for an email preview. You should take tadalafil one time a day. Medicines that block an enzyme called CYP3A4. It belongs to the drug class known as PDE5 inhibitors. This will increase the supply of blood to the lungs and reduce the workload of the heart. Talk to your doctor about which dosing schedule is right for you.Cialis works by increasing blood flow to the penis to help a person get and maintain an erection. It also blocks the PDE5 enzyme, which enhances the effects of nitric oxide . The four main medicines taken by mouth for erectile dysfunction are: Avanafil (Stendra). Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 . Cialis is used to treat erectile dysfunction (impotence) and symptoms of benign prostatic hypertrophy (enlarged prostate). Another brand of tadalafil is Adcirca, which is used to .