The Chemical Imbalance Theory of Depression: What the Evidence Actually Says, and Why It Matters in the Clinic

Few ideas in modern medicine have travelled so far on so little evidence as the "chemical imbalance theory" of depression. For a generation of patients, it was the lay-language summary of why they felt unwell and why a small white tablet was supposed to help: depression, they were told, is caused by a deficiency of serotonin in the brain, and antidepressants correct that deficiency. The story is tidy, intuitive, and reassuringly biological. It is also, on the strongest available reading of the evidence, not true.