It is! Massively so! For example, one of the treatments for schizophrenia in the 1920s/30s was insulin coma therapy. They would inject patients with insulin until their blood sugars dropped low enough to send them into a coma. They were then revived with a glucose injection and this was repeated over a few days/weeks, except there was a risk of brain damage and 1 in a hundred died. And lobotomies were carried out for major depression as recently as the 1970s
