January 11, 1922

Discovery of insulin

Leonard Thompson receives the first injected pancreatic extract; the trial fails

The historic first injection was a failure. It barely moved the boy's blood sugar and left him with a sterile abscess.

11 January 1922, Toronto General Hospital

On 11 January 1922 the house physician Ed Jeffrey injected Leonard Thompson with 15 cc of a beef-pancreas extract prepared by Frederick Banting and Charles Best, under the clinical direction of Walter Campbell. Thompson's family had consented to the experimental treatment.

The injections went into Thompson's buttocks, and the preparation was recorded as "Macleod's serum."

Thompson weighed under 65 pounds and was surviving on a restricted diet of 450 calories a day.

What the extract did

His blood sugar fell only from 0.440% to 0.320%, and twenty-four-hour urinary glucose from 91.5 grams to 84 grams. The ketones did not clear and there was no visible clinical improvement.

The impurities produced a sterile abscess. Clinicians judged the reaction to outweigh the modest biochemical effect and stopped further injections of that preparation.

The success came twelve days later

On 19 January James Bertram Collip found a better purification method, and on 23 January Campbell administered Collip's extract to Thompson, whose blood sugar fell to normal within a day and whose condition improved markedly.

The listed event conflates the two dates: 11 January is securely the first injection of the Toronto extract into a human, but the first unambiguously successful human treatment was 23 January.

The Toronto group was not yet consistently calling the material insulin — contemporary records used pancreatic extract, "Macleod's serum" and "isletin" — and adopted the name in a paper prepared in May 1922.

Sources

Researched 23 Aug 2026 5 sources 2 audit passes Date disputed

How this was checked

Researched from the web into a fact sheet, rewritten from that sheet, then audited against it by a different model. How the pipeline works →

Date disputed. Sources disagree about when this happened.

What the sources leave uncertain

The listed event conflates two dates. January 11 is securely documented as the first injection of the Toronto pancreatic extract into a human, but the first unambiguously successful human treatment occurred on January 23.
Sources commonly call Thompson fourteen, including the University of Toronto exhibits. Because he was born in July 1908, he was thirteen by completed years on 11 January 1922; the discrepancy reflects historical age-reporting rather than uncertainty about his identity.
The Toronto group was not yet consistently calling the material “insulin.” Contemporary records used terms including pancreatic extract, “Macleod’s serum,” and “isletin”; the group adopted “insulin” in a paper prepared in May 1922.