ED is the inability to develop and maintain an erection for satisfactory sexual intercourse or activity. ED is a highly prevalent medical condition often associated with multiple causes. It is estimated that more than 50 million American men suffer from mild/moderate to severe ED. Roughly 50% of men in their 50's, 60% of men in their 60's, and 70% of men in their 70's suffer from ED. The economic impact of ED is in the billions of dollars. More than 5 billion dollars a year are spent on the pro-erectile medications currently in the market.