The generic versions are just as effective and much less expensive. In addition, ED is extremely common. An erection results from an increase in blood flow to the penis. This information is reviewed by a licensed practitioner who will assess your eligibility for the medication. However, all medications come with risks. Finally, we checked customer reviews to better understand user experiences with each platform.$ Get free savings. Online Pharmacy & OTC Our 12 Picks for Online Pharmacies of If you need medication delivered here are the best online pharmacies—and how to choose the right one for you By Natalie Rahhal Updated on April 21, Medically reviewed by Chris Vincent, MD Fact checked by James Lacy Print. Viagra and Cialis are the most popular ED (erectile dysfunction) drugs in the world, but they’re not the only ones. They’re equally safe and effective, but they differ a bit in how fast they work, how long they last, and how much they cost. Here’s what you need to know.