[3][4] During his years in Birmingham and Edinburgh, John Berry Haycraft had been actively engaged in research and published papers on the coagulation of blood, and in 1884, he discovered that the leech secreted a powerful anticoagulant, which he named hirudin, although it was not isolated until the 1950s, nor its structure fully determined until 1976.

[8] Therefore, hirudin prevents or dissolves the formation of clots and thrombi (i.e., it has a thrombolytic activity)[citation needed], and has therapeutic value in blood coagulation disorders, in the treatment of skin hematomas and of superficial varicose veins, either as an injectable or a topical application cream.

In some aspects, hirudin has advantages over more commonly used anticoagulants and thrombolytics, such as heparin, as it does not interfere with the biological activity of other serum proteins, and can also act on complexed thrombin.

It is difficult to extract large amounts of hirudin from natural sources, so a method for producing and purifying this protein (specifically P01050 in the infobox) using recombinant biotechnology has been developed.

This has led to the development and marketing of a number of hirudin-based anticoagulant pharmaceutical products, including: Several other direct thrombin inhibitors are derived chemically from hirudin.