Viagra was supposed to be a treatment for the heart condition angina, but during clinical trials an unexpected side effect was noticed by the young male participants.

Telling the story of this unexpected discovery, presenter Adam Hart speaks with the Pfizer scientists Sir Simon Campbell and Dr Peter Ellis who were part of the team that noticed the unusual side effects, and brought Viagra forward as a treatment for erectile dysfunction.

Sex journalist Alix Fox discusses the importance of this little blue pill to patients. This is the story of the accident that changed sex.

Produced by Rory Galloway. First broadcast on Monday 23 July 2018.