Doctors bought the story line that all depression results from a chemical imbalance in the brain and therefore requires a chemical fix—the prescription of an antidepressant medication. This is absolutely true for severe depressions, absolutely false for most milder ones. The proof of this pudding is that psychotherapy is just as effective as medication for milder depressions, and neither has a big edge over placebo. Millions of people take medicine they don’t need for a diagnosis of MDD that they don’t really have, on the false assumption of chemical imbalance.
Allen Frances, M.D, "Saving Normal," p.155