chemical imbalance
Meaning of chemical imbalance: A phrase used in two quite different ways: a measurable disturbance in body chemistry, and a loose shorthand for mental illness.
Definition of chemical imbalance
Chemical imbalance describes a state in which a substance the body relies on is present in too great or too small an amount. Used precisely it refers to measurable disturbances, such as abnormal levels of sodium, potassium, calcium, glucose or thyroid hormone. Used loosely it is a popular shorthand for the idea that mental illness arises from a shortage of a single brain messenger.
What does it mean in the laboratory sense?
Here the phrase is precise and testable, because the substance can be measured in blood.
| Substance | What a disturbance can produce |
|---|---|
| Sodium | Confusion, drowsiness, seizures when it falls quickly |
| Potassium | Muscle weakness and disturbed heart rhythm |
| Calcium | Cramps and tingling when low; thirst and confusion when high |
| Glucose | Sweating, tremor and confusion when low |
| Thyroid hormone | Fatigue and cold intolerance, or agitation and weight loss |
Causes include kidney disease, hormone-producing tumors, vomiting and diarrhea, and a wide range of medicines. A chemical disturbance of this kind is identified by testing, not by inference.
Where does the phrase come from in mental health?
It grew out of a reasonable observation followed by a shaky inference. Drugs that raise levels of serotonin, noradrenaline or dopamine were found to change symptoms of depression and psychosis. From that came the suggestion that a deficiency or excess of those messengers caused the illness in the first place. The idea was easy to explain, and it offered an account of mental illness as a physical condition rather than a personal failing, which is part of why it spread so widely.
How well does the shorthand hold up?
Poorly, as a complete explanation. No test measures a messenger imbalance in a living brain, and reviews of the accumulated evidence have not supported a simple shortage of one messenger as the cause of depression. Current accounts describe interacting genetic, biological, psychological and social contributions, with brain messengers as one part of a larger picture. The same reasoning was applied to dopamine in schizophrenia and has been revised in similar ways. That a medicine changes symptoms says what the medicine does; it does not establish what started the illness.
Used in a sentence
The assessment looked for a chemical imbalance capable of explaining the sudden confusion.
Good to know
That a medicine acting on a brain messenger relieves symptoms does not establish that a shortage of that messenger caused them, and no test measures such an imbalance in a living brain.