Make sure to get an estimate of when you can expect your prescription in the mail. If approved, the provider will issue a prescription. What Are the Symptoms of Erectile Dysfunction? Here are some key factors to consider when deciding: Pricing: Know how much your monthly supply will cost with shipping and tax. Most erectile dysfunction medications belong to the drug class known as PDE5 inhibitors , which help relax the muscles and increase blood flow to allow for a full erection. Also, look into whether expediting is offered.Q&A Drug Images What is Viagra? If you have erectile dysfunction (ED), your doctor may recommend that you take Viagra. It’s a prescription drug that’s used in adult males* with . Sildenafil (Viagra brand) increases blood flow to the penis following sexual stimulation. It does this by blocking the enzyme responsible for the breakdown of cGMP. cGMP is a . Sildenafil (Viagra) and tadalafil (Cialis) are the most commonly prescribed medications for ED, and they have the longest track record. For occasional use, most people start with .