The first PDE5 inhibitor to hit the market was Viagra, which won FDA approval in 1998. Its active ingredient is sildenafil. Pfizer, the drug’s manufacturer, discovered its ability to facilitate erections by accident while testing a sildenafil compound for the treatment of angina and high blood pressure. While it was only minimally successful at easing the symptoms of angina, the drug readily induced erections in many of the test subjects.
Introduced in 2003, Cialis (tadalafil) was the next PDE5 inhibitor to reach the market. As originally marketed, the pill was longer lasting than Viagra, retaining its effectiveness for up to 36 hours. Five years later, a lower-strength formulation of Cialis came to market. Available in 2.5- and 5-milligram tablets, Cialis for Daily Use is taken daily so that users can achieve an erection whenever the time is right.
Rounding out the family of PDE5 inhibitors are Levitra (vardenafil), which also debuted in 2003; orally soluble Staxyn (vardenafil), approved in 2010; and Stendra (avanafil), approved in 2012.