Answer: Warfarin

The heart medication warfarin, sold primarily under the brand name Coumadin in the United States, is a heart drug dating back to the 1950s. How warfarin became a commonly prescribed blood thinner for patients with heart conditions, however, isn’t as simple as “Well, back in the 1950s they made it in a lab.”, but is instead a winding 20th century journey.

In the early 1920s, there was an outbreak of a previously unrecognized cattle disease in the northern U.S. and Canada: cattle were hemorrhaging blood after minor medical procedures and sometimes even spontaneously. The source of the disease was traced, through research conducted by Canadian veterinary pathologist Frank Schofield, to the cattle eating moldy silage derived from sweet clover crops and that something within the crops was acting as a very powerful anticoagulant agent.

While he was able to conclusively show it was the moldy sweet clover that did the animals in, the mechanism of action was unclear. It wasn’t until a series of experiments in the 1930s at the University of Wisconsin isolated the anticoagulant in the spoiled silage that researchers were able to make headway in giving the compound, dicoumarol, a chance at being used for practical applications.

The first practical application wasn’t treating heart patients, however, but as a rodenticide. The first commercial application of the compound, in 1948, was on farms and in cities killing off rodents. Warfarin is odorless and tasteless, which makes it perfect for mixing into bait stations to poison rats and mice. It wasn’t until 1954 that the drug was first used as a blood thinner in humans, but it quickly gained widespread acceptance. By 1955, it was considered so safe that it was prescribed to President Eisenhower after his heart attack.