On Mar. 27, 1998. the Pfizer drug Viagra (Sildenafil) was approved by the U.S. Food and Drug Administration (FDA) to treat erectile dysfunction. The drug was discovered in 1989 while scientists looking for a treatment for heart-related chest pain.

Within 6 months of approval by the FDA, 5.3 million prescriptions were written for sildenafil citrate. It represented the first clearly effective and FDA-approved oral therapy for the treatment of ED. The chemical structure of sildenafil is very similar to the cyclic guanosine monophosphate molecule with which it competes, in the enzyme phosphodiesterase type-5. Sildenafil binds to the phosphodiesterase-5 enzyme, preventing the breakdown of cyclic guanosine monophosphate through competitive inhibition.

There is no doubt that the discovery and development of sildenafil has been a revolutionary event in medicine and society. The discovery was paved by the Nobel prizewinning efforts of Drs. Furchgott, Ignarro, and Murad, who discovered the link between nitric oxide (NO) and the human cardiovascular system. NO is the neurotransmitter that signals the nutrient blood vessels of the heart to relax and increase their flow.

The use of sildenafil in female sexual dysfunction (FSD) is controversial. FSD is not as easily measured as ED. Many of the objective tests do not correlate with perceptions of the patients. Nonetheless, sildenafil has been shown to be effective in reversing the sexual dysfunction side effects of SSRIs in females, sexual arousal disorders, and spinal cord injury-induced sexual dysfunction. Large-scale trials are needed better to define the role of sildenafil in FSD.

In 2017, Viagra became available as a generic medication in the UK.