“Depression, we are told over and over again, is a brain disease, a chemical imbalance that can be adjusted by antidepressant medication. In an informational brochure issued to inform the public about depression, the US National Institute for Mental Health tells people that 'depressive illnesses are disorders of the brain' and adds that 'important neurotransmitters - chemicals that brain cells use to communicate - appear to be out of balance'. This view is so widespread that it was even proffered by the editors of PLoS [Public Library of Science] Medicine in their summary that accompanied our article. 'Depression,' they wrote, 'is a serious medical illness caused by imbalances in the brain chemicals that regulate mood', and they went on to say that antidepressants are supposed to work by correcting these imbalances.
The editors wrote their comment on chemical imbalances as if it were an established fact, and this is also how it is presented by drug companies. Actually, it is not. Instead, even its proponents have to admit that it is a controversial hypothesis that has not yet been proven. Not only is the chemical-imbalance hypothesis unproven, but I will argue that it is about as close as a theory gets in science to being dis-proven by the evidence.”
The Emperor's New Drugs: Exploding the Antidepressant Myth