There are true chemical imbalances in the body; but when they are present, the condition is no longer labeled chemical imbalance. It is labeled according to the chemical that is out of balance, and it is given a medical disease label. Low thyroid is a chemical imbalance, but it is called “hypothyroid” instead of “chemical imbalance.” Low potassium is a chemical imbalance, but it is called “hypokalemia.” High blood sugar is a chemical imbalance, but it is called “diabetes.” When people talk about “chemical imbalance” as a cause for depression, it is because there are no laboratory tests to prove this. Remember, an illness means something is wrong in the tissues of the body. If there is truly something wrong with the body, it can be proved by objective tests performed by an objective observer. The reality is that there are no laboratory tests that can prove the presence of a chemical imbalance. The chemical imbalance diagnosis of an illness is not proven by tests, but is based on what a person thinks and feels as described by DSM-IV (Diagnostic and Statistical Manual of Mental Disorders, fourth edition). Whenever the term “chemical imbalance” is used, it is as a generic term without proof that any change is present in any chemical."
Robert D. Smith, M.D., The Christian Counselor’s Medical Desk Reference, p.66