Insulin was discovered in 1921 by Frederick Banting and Charles Best, working in a small laboratory at the University of Toronto. Within months, their crude pancreatic extract went from keeping diabetic dogs alive to saving the life of a dying 14-year-old boy. It remains one of the fastest translations from laboratory idea to life-saving treatment in medical history.
Diabetes Before Insulin
To understand why the discovery mattered so urgently, you need to know what a diabetes diagnosis meant in 1920. For children and young adults with what we now call type 1 diabetes, it was a death sentence. Most children diagnosed under age ten died from diabetic coma within months to a few years.
The best available treatment was the “Allen starvation diet,” named after physician Frederick Allen. Patients were put through extended fasts, then kept on severely restricted calories. An 11-year-old girl named Elizabeth Hughes, who would later become one of insulin’s most famous recipients, was placed on a week of total fasting followed by 500 calories a day with one fasting day per week. A seven-year-old boy was discharged on 700 calories daily. A four-year-old lived on 980 calories. These diets could eliminate sugar in the urine and extend life by a year or so, but patients slowly wasted away. The treatment essentially traded one form of dying for another, slightly slower one.
The Idea That Started Everything
On the night of October 30, 1920, Frederick Banting, a young surgeon with no research experience, read an article by Moses Baron describing how blocking the pancreatic duct with gallstones caused certain cells in the pancreas to wither and die while leaving other cells, the islets of Langerhans, intact. Scientists had long suspected that the islets produced some internal secretion that regulated blood sugar, but every attempt to extract it failed. The pancreas is full of powerful digestive enzymes, and those enzymes destroyed the delicate hormone during extraction.
Banting’s insight was simple: if you surgically tied off the pancreatic duct, the enzyme-producing cells would degenerate over time, but the islets would survive. You could then harvest the pancreas and extract the hormone without digestive enzymes destroying it in the process. He brought this idea to J.J.R. Macleod, a respected diabetes researcher at the University of Toronto. Macleod was skeptical but gave Banting lab space, ten dogs, and a medical student named Charles Best as an assistant.
A Summer of Grueling Experiments
Banting and Best began working in May 1921, through the heat of a Toronto summer. Their approach had two steps: first, surgically remove a dog’s pancreas to make it diabetic; second, inject it with extract from a duct-ligated pancreas and see if blood sugar dropped. The work was messy, technically difficult, and full of failure. Dogs died from surgical complications. Extracts varied wildly in potency. Their supply of duct-ligated donor dogs was nearly depleted by mid-August.
But scattered among the failures were clear successes. They managed to keep one depancreatized dog alive and in good condition for eight days using extract from five degenerated pancreases. Blood sugar levels dropped after injections and rose again when treatment stopped. The pattern was unmistakable: something in those islet cells controlled blood sugar, and they could extract it.
The pair also discovered they didn’t strictly need the duct-ligation technique. Extract from fetal calf pancreases, where the enzyme-producing cells hadn’t yet fully developed, worked as well. This was a critical practical finding, because it meant the hormone could potentially be sourced from slaughterhouse material rather than requiring weeks of surgical preparation in dogs.
Making It Safe for Humans
The crude extract that worked in dogs was far too impure for people. Processing pancreatic tissue and its enzymes was extremely difficult, and previous attempts by other researchers had produced results too toxic for practical use. In December 1921, Macleod brought biochemist James Collip onto the team to solve this problem.
On the night of January 19, 1922, working alone late in the lab, Collip found the key. By using a succession of different concentrations of alcohol, he discovered he could trap the active hormone in a semipure form, separating it from the proteins and other contaminants that caused dangerous reactions. It was a breakthrough in biochemistry, though Collip’s exact method was so delicate that he himself briefly lost the ability to reproduce it in subsequent weeks, causing a panicked stretch in the lab.
The First Human Injection
Leonard Thompson was 14 years old, weighed just 65 pounds, and was dying of diabetes at Toronto General Hospital. On January 11, 1922, he became the first person to receive an injection of pancreatic extract. It didn’t go well. Fifteen milliliters of the extract barely lowered his blood sugar, did nothing for his dangerous ketoacidosis, and caused a sterile abscess at the injection site.
Twelve days later, on January 23, Thompson received a second round of injections, this time using Collip’s purified extract. The results were dramatic. His blood sugar dropped from 520 mg/dl to 120 mg/dl, a plunge from life-threateningly high to near-normal. Sugar in his urine fell from 71 grams to 9 grams. The acidic compounds poisoning his blood disappeared entirely. Leonard Thompson lived another 13 years, dying in 1935 of pneumonia at age 27.
Scaling Up Production
Word spread quickly. Interest in the extract and requests for insulin were growing even before Banting and Best published their first paper in February 1922. But making enough insulin to treat more than a handful of patients was a serious engineering challenge. The University of Toronto’s in-house labs simply couldn’t produce it at scale.
By May 1922, the university reached an agreement with Eli Lilly and Company, an American pharmaceutical firm. Lilly’s engineers redesigned the extraction process for industrial production, and by late summer, enough insulin was being manufactured to expand trials to clinics across North America. The university and Lilly clashed over how quickly to release the drug to the public. Toronto wanted to keep distribution limited while safety data accumulated. General distribution finally began in the fall of 1923. In its early days, insulin was extracted from bovine and porcine pancreases collected from slaughterhouses, a sourcing method that would continue for decades.
The Nobel Prize and Its Controversies
In 1923, just two years after the summer experiments on dogs, the Nobel Prize in Physiology or Medicine was awarded jointly to Frederick Banting and J.J.R. Macleod “for the discovery of insulin.” The decision immediately sparked one of the most famous disputes in Nobel history.
Banting was furious that Macleod, who had been away in Scotland for much of the critical experimental work, received the prize instead of Charles Best, the student who had actually performed the experiments alongside him. Banting publicly announced he would split his share of the prize money with Best. Macleod, in turn, split his share with Collip. The question of who deserved credit for insulin’s discovery has never been fully settled. Banting had the original idea and did the grueling lab work. Best was his hands-on partner through every experiment. Macleod provided the lab, the intellectual framework, and the scientific credibility that made publication and acceptance possible. Collip solved the purification problem that made human treatment feasible.
What is settled is the result. Before 1922, a diagnosis of type 1 diabetes in a child was a slow death sentence measured in months. After insulin, it became a manageable chronic condition. Few discoveries in medicine have ever drawn so sharp a line between before and after.