They enhance the effects of a chemical the body makes that relaxes muscles in the penis, called nitric oxide. Erectile dysfunction can be caused by a variety of factors , including age, cardiovascular problems, diabetes, and other conditions that affect nerve function or blood flow. A phone or video consultation is sometimes required for legal purposes. When oral medications might not be safe Check with your health care team before you take any medicine for erectile dysfunction. Cialis tadalafil : This ED medication works with the same principle as Viagra, but lasts up to 36 hours.Avanafil (Stendra). Sildenafil (Viagra). Tadalafil (Cialis). Vardenafil. These medicines are called PDE5 inhibitors. They enhance the effects of a chemical the body . Best Low Cost: GoodRx Fastest Delivery: Blink Health: Sesame Sign Up Now Key Specs Cost: Consultation prices vary based on the prescriber; $5 generic . Published on October 18, warning This article is no longer being updated and some information may not be current.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. .