Tadalafil is in a class of medications called phosphodiesterase PDE inhibitors. Tadalafil does not prevent pregnancy or the spread of sexually transmitted diseases such as human immunodeficiency virus HIV. People with kidney or liver problems will need to either take a lower dose of Cialis or avoid the medication altogether, depending on the severity of the condition. It belongs to the drug class known as PDE5 inhibitors. They include dutasteride Avodart, Jalyn and finasteride Propecia, Proscar. As with sildenafil, a high-fat meal or alcohol keep the body from absorbing it as quickly. Dosing Guidelines Typical Cialis dosages will differ depending on the conditions it’s prescribed to treat as well as other factors. · Cialis; Descriptions. Tadalafil is used to treat men who have erectile dysfunction (also called sexual impotence). Tadalafil belongs to a group of medicines called phosphodiesterase 5 (PDE5) inhibitors. These medicines prevent an enzyme called phosphodiesterase type-5 from working too quickly. The penis is one of the areas where . The four main medicines taken by mouth for erectile dysfunction are: Avanafil (Stendra). Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. They enhance the effects of a chemical the body makes that relaxes muscles in the penis, called nitric oxide. Published on October 18, warning This article is no longer being updated and some information may not be current. Visit the GoodRx Healthhomepage for our latest articles. .