Insulin shock therapy was a form of treatment that involved administering large doses of insulin to patients suffering with mental disorders such as schizophrenia and depression, in order to induce a coma like state due to low blood sugar (Fink, 1999). 

The theory behind this therapy was that by resulting insulin, the shock to the body would have a therapeutic effect on the patient's mental state.

Insulin shock therapy was considered a major advance in the treatment of mental disorders in the early 1900s, and was used extensively in psychiatric hospitals and institutions throughout the world (Fink, 1999). 

with the developments of new and more effective treatments for mental disorders and mental illnesses along with the plethora of safety issues and side effects caused by insulin shock therapy, the use the therapy declined heavily in the mid-20th century.