Hirudin: An anticoagulant ("bloodthinner"). Hirudin is the active principle in the salivary secretion of leeches. The name hirudin is from Hirudo medicinalis, the name of the medicinal leech.
In 1884 John Haycraft in Strasbourg found that leeches contained a substance with anticoagulant properties. This anticoagulant in leech saliva was isolated in the 1950s and found to be an antithrombin (an inhibitor of thrombin). The primary chemical structure of hirudin was determined in 1976.
The anticoagulant drugs desirudin and lepirudin (brand name: Refludan) are genetically engineered recombinant forms of hirudin.