Viagra can be taken as long as four hours or as little as 30 minutes before sex. Emling S. However, others work on a cash-pay basis and don’t partner with insurance companies. These PDE5 inhibitors may cause headache, flushing, drop in blood pressure, or other adverse effects. Insurance can help you save even more on consultations and medications. How oral medicines differ Each oral medicine for ED has a slightly different chemical makeup. What Are the Symptoms of Erectile Dysfunction?Introduction If you’re looking at treatment options for erectile dysfunction (ED), you may want to learn more about Cialis and its cost. It’s a prescription drug used to treat . 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 . Published on October 18, warning This article is no longer being updated and some information may not be current.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. .