Psychiatrist Thomas Szasz was (and is) sometimes wrongly accused of denying that mental illnesses exist. However, what he actually said is that many (not all) instances of mental illness are the consequence of attempts to confront and tackle the problem of how to live, and that to identify such instances as a disease or illness is to hide the very real problems in living that people face.
In this article he gave (amongst other things) a potted history of psychiatry. 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. Hannah Arendt was right when she observed: ‘There are no limits to the possibilities of nonsense and capricious notions that can be decked out as the last word in science.’
The idea that mental illness is a bodily disease dates back to the premodern medical conception of disease as a ‘humoral imbalance,’ comically prefiguring the modern, supposedly scientific conception of it as ‘chemical imbalance.’ In the United States, the idea of mental illness as humoral imbalance was famously espoused by Benjamin Rush (1746-1813), the founding father American psychiatry. Rush did not discover that certain behaviors are diseases; he decreed that they are: ‘Lying,’ he declared, ‘is a corporeal disease.’ In a letter to his friend, John Adams, he wrote: ‘The subjects [mental diseases] have hitherto been enveloped in mystery. I have endeavored to bring them down to the level of all other diseases of the human body, and to show that the mind and the body are moved by the same causes and subject to the same laws.’
In the nineteenth century, the scientific concept of disease as lesion replaced the Galenic concept of disease as humoral imbalance. Now, physicians postulated that mental diseases are diseases of the brain. From about 1850 until past World War I, German (more precisely, German-speaking) psychiatry ruled the field. The very term psychiatry (Psychiatrie) was a German invention, coined by Johann Christian Reil (1759-1813) in 1808. Reil, not an alienist (psychiatrist), was one of the outstanding medical scientists and physicians of his age. He was a friend and physician of Johann Wolfgang von Goethe. In addition to coining the term ‘psychiatry,’ he also coined the term ‘noninjurious torture,’ to describe the methods of frightening mental patients that he considered effective and legitimate ‘treatments.’ …”
You can read more from here.