Insulin was discovered in 1921 by Sir Frederick G. Banting, Charles H. Best, and John J.R. Macleod at the University of Toronto. Banting, a Canadian surgeon, and Best, a medical student, successfully isolated insulin from the pancreas of dogs, with Macleod providing laboratory support and guidance. Later, James B. Collip purified the extract further to make it suitable for human use. The first successful insulin injection in a human was given in January 1922 to Leonard Thompson, a 14-year-old boy with type 1 diabetes, marking a breakthrough in diabetes treatment

. Although Banting and Macleod received the 1923 Nobel Prize in Physiology or Medicine for the discovery, Banting shared his prize money with Best in recognition of his crucial role. The discovery is considered one of the greatest medical breakthroughs, saving millions of lives worldwide

. It is worth noting that Romanian scientist Nicolae Paulescu had earlier developed a pancreatic extract called pancreine in 1916, which had antidiabetic effects in dogs. He patented his method in 1922 and claimed priority over the discovery of insulin, but his claims were not recognized by the Nobel committee. Nonetheless, Paulescu's contributions are acknowledged as significant in the history of insulin research