[3] Other side effects may include pain or skin changes at the sites of injection, low blood potassium, and allergic reactions.

[10] Hans Christian Hagedorn (1888–1971) and August Krogh (1874–1949) obtained the rights for insulin from Frederick Banting and Charles Best in Toronto, Canada.

In 1923 they formed Nordisk Insulin laboratorium, and in 1926 with August Kongsted he obtained a Danish royal charter as a non-profit foundation.

In 1936, Hagedorn and B. Norman Jensen discovered that the effects of injected insulin could be prolonged by the addition of protamine obtained from the "milt" or semen of river trout.

University of Toronto, Canada later licensed protamine zinc insulin (PZI),[11] to several manufacturers.

[medical citation needed] Synthetic "human" insulin is also complexed with protamine to form NPH.