Warfarin, sold by Bristol Myers Squibb (BMY) as Coumadin, a blood thinner used to stave off strokes and heart attacks, was a rat poison until its lower-dose benefit to humans was stumbled upon.
The actual discovery of Warfarin was itself surprising. Back in 1933, a Wisconsin farmer dropped in on Professor Karl Paul Link of the University of Wisconsin-Madison's School of Agriculture and asked for his help in figuring out why local cows were dying.The suspect was the type of hay the cows were eating and the type of sweet clover added to the feed. It took Link and his lab until 1941 to fully identify and isolate the powerful anticoagulant killing the cattle. In marketing the chemical as a rat poison, the name Warfarin was chosen as a shout out to the Wisconsin Alumni Research Foundation, an organization that helps process, patent and commercialize inventions by UW-Madison faculty and staff.