Insulin is a hormone that regulates blood sugar, and its isolation was a significant achievement in medical history. Before the 1920s, a diagnosis of what is now known as Type 1 diabetes was a death sentence. The discovery of insulin transformed this fatal condition into a manageable one, offering life to millions. This breakthrough was the result of dedicated research that culminated in a transformative moment for a patient on the brink of death.
Life Before Insulin
Before 1922, medicine had no effective answer for Type 1 diabetes. Physicians understood the disease was related to the pancreas but lacked the means to replace its missing internal secretion. The only available treatment was a strict dietary regimen, pioneered by figures like Dr. Frederick Allen. These “starvation diets” were extremely low in carbohydrates, forcing the body into undernutrition to minimize blood sugar levels.
While this approach could extend a patient’s life by a year or two, it was not a cure. Patients, many of them children, became gaunt and frail as their bodies were deprived of necessary energy. The diets sometimes prescribed as few as 450 calories a day, meaning patients could succumb to starvation itself. This situation created an urgent need for a therapeutic intervention.
The Discovery in Toronto
The breakthrough occurred at the University of Toronto during the summer of 1921. A surgeon, Frederick Banting, had an idea about how to isolate the internal secretion of the pancreas. He theorized that by ligating the pancreatic ducts of a dog, the digestive enzyme-producing parts of the organ would degenerate. This would leave the cells responsible for the anti-diabetic secretion intact for extraction.
Banting presented his idea to Professor J.J.R. Macleod, an expert in carbohydrate metabolism. Though initially skeptical, Macleod provided Banting with laboratory space, ten test dogs, and the assistance of a medical student, Charles Best. That summer, Banting and Best successfully induced diabetes in dogs by removing their pancreases. They then treated them with an extract from the degenerated pancreases of other dogs, which proved capable of lowering blood sugar levels in the animals.
As their work progressed, it became clear a more refined extract was needed for human trials. Macleod enlisted the help of James Collip, a skilled biochemist, to purify the pancreatic extract. Collip’s expertise was key in developing a method to produce a purer, more stable form of the substance. Banting named it “insulin,” from the Latin word “insula” (island), referencing the islet cells of the pancreas where it is produced.
Leonard Thompson’s First Injections
The first human trial took place in January 1922 at the Toronto General Hospital. The patient was Leonard Thompson, a 14-year-old boy who was near death from diabetes, having wasted away to just 65 pounds. His parents consented to the experimental treatment. On January 11, 1922, Leonard received his first injection of the extract prepared by Banting and Best.
This initial attempt was not a success. While it did cause a slight drop in his blood sugar, the extract was too impure. Leonard suffered a severe allergic reaction and developed an abscess at the injection site. With minimal clinical benefit, the trial was considered a failure and the injections were stopped.
Following this setback, James Collip worked intensely to improve the purification process. For nearly two weeks, he refined his method for removing contaminants from the beef pancreas extract. On January 23, 1922, the team was ready to try again with the new, purer extract.
This time, there was no significant allergic reaction. Leonard’s blood sugar levels dropped from a dangerously high 520 mg/dL to a near-normal 120 mg/dL within 24 hours. His condition improved remarkably; his medical records noted he “became brighter, more active, looked better and said he felt stronger.”
The success of this second injection was the turning point, demonstrating that insulin could safely reverse the fatal course of diabetes. Leonard Thompson, who had been on the verge of death, would live for another 13 years on insulin treatments.
From Breakthrough to Mass Production
The success with Leonard Thompson transformed the experimental extract into a life-saving therapy. Recognizing the potential of their discovery, the Toronto team moved to ensure it would be widely available. Banting, Best, and Collip sold the patent for insulin to the University of Toronto for a symbolic one dollar each. This was driven by the principle that the treatment should belong to the world, not be a source of private profit.
With the patent secured for public benefit, the next hurdle was production. The university’s laboratories could not produce insulin on the scale needed to treat the thousands of people with diabetes. To solve this, the university partnered with the pharmaceutical company Eli Lilly and Company. This collaboration was for developing methods to mass-produce a pure and stable form of insulin from the pancreases of cattle and pigs.
By 1923, just a year after Leonard’s successful injection, insulin was becoming widely available across North America and beyond. In recognition of this achievement, the 1923 Nobel Prize in Physiology or Medicine was awarded to Frederick Banting and J.J.R. Macleod. Banting immediately chose to share his prize money with his assistant, Charles Best. Macleod, in turn, shared his with the biochemist James Collip, acknowledging the collaborative effort.