Heparin is a naturally occurring anticoagulant that prevents the formation of blood clots. Heparin does not itself break down existing clots, but enhances the body’s natural mechanisms involved in dissolving clots.

Heparin is one of the oldest medicines currently in use. It was first discovered in 1916 before the United States Food and Drug Administration had been established and it did not enter clinical trials until 1935.

Heparin was first discovered by Jay McLean and William Henry Howell. McLean was a second-year medical student at Johns Hopkins University who was assisting Howell in the investigation of pro-coagulant preparations. McLean isolated a fat-soluble anticoagulant in canine liver tissue in 1916. In 1918, Howell called the anticoagulant heparin, based on the Greek word for liver, “hepar.” McLean’s findings probably influenced the work of Howell and team, which eventually led to the polysaccharide being discovered.

In the 1930s several researchers started to explore heparin and in 1935 Erik Jorpes from the Karolinska Institutet published his report on the molecule’s structure. This made it possible for the first heparin product to be manufactured and released for intravenous use by the Swedish company Vitrum AB in 1936. Connaught Medical Research Laboratories then refined the production of heparin to give a safe, nontoxic version that could be administered in saline solution.

In May 1935, the first human trials of heparin were conducted and Connaught’s heparin was confirmed as a safe, easily-available and effective blood anticoagulant.