Doctors first successfully treated a patient with insulin for severe diabetes in 1922.
The patient was Leonard Thompson, a 14-year-old boy at Toronto General Hospital who was near death from diabetes. The first extract prepared for him caused an allergic reaction because it was impure, but a refined preparation was given successfully later in January 1922.
Frederick Banting and Charles Best had worked on extracting the pancreatic hormone, while J. J. R. Macleod supervised the research and James Collip helped purify the preparation. Their work transformed diabetes from a commonly fatal disease into a treatable chronic condition.
Insulin is a hormone that helps cells take up glucose from the blood. It is not a cure for every form of diabetes, and modern treatment includes purified human insulin and engineered insulin analogues. The 1922 breakthrough concerned therapeutic insulin, not the discovery of glucose itself.