“There was no evidence for a humoral imbalance causing illness, but the doctrine prevailed for two thousand years. There is no evidence for a chemical imbalance causing mental illness, but that does not impair the doctrine’s scientific standing or popularity.”
This article, written by psychiatrist Thomas Szasz in 2006, is well worth reading in terms of the historical perspective that it provides, though some of his conclusions are starkly expressed in controversial terms. It begins:
“A 1999 White House Conference on Mental Health concluded: ‘Research in the last decade proves that mental illnesses are diagnosable disorders of the brain.’ President William Clinton was more specific: ‘Mental illness can be accurately diagnosed, successfully treated, just as physical illness.’ Persons who reject the view that mental illnesses are physical diseases are dismissed by today’s opinion-makers as intellectual troglodytes, on a par with ‘flat-earthers.’
That the claim that ‘mental illnesses are diagnosable disorders of the brain’ is a lie ought to be evident to anyone who thinks for himself. Here I want to show that the claim that ‘research in the last decade proves [this]’ is also a lie, one more in a very long list in the history of psychiatry. The contention that mental illness is brain disease is as old as psychiatry itself: it is an integral part of the grand lie that psychiatry is a branch of medicine and healing, when in fact it is a branch of the law and social control …”
You can read more here.