Heinz Edgar Lehmann OC FRSC (July 17, 1911 – April 7, 1999) was a German-born Canadian psychiatrist best known for his use of chlorpromazine for the treatment of schizophrenia in 1950s and "truly the father of modern psychopharmacology.

No one at that time had been able to understand or help psychotic and depressed patients, who filled mental hospitals around the world, so when the first big breakthrough chlorpromazine(Largactil) arrived from France in 1953 and then imipramine (Tofranil), which came from German-speaking Switzerland in 1958, they both showed promise.

In 1961 Dr. Lehmann became involved in a new US Public Health Service Program initiative which met to exchange observations and findings on new psychotropics.

[4] Their findings and observations were shared internationally in articles and at conferences and had a profound impact on the evolution of psychopharmacology as a discipline.

In 1973, he was a member of the Nomenclature Committee of the American Psychiatric Association that decided to drop homosexuality from the Diagnostic and Statistical Manual of Mental Disorders, i.e. to depathologize it.