Eli5: why is there no test for the “chemical imbalance” that is often mentioned for depression?
In: Chemistry
It is a simplification that doctors use to help people understand why drugs can help treat depression. The exact mechanisms behind depression are complex and poorly understood, and likely to vary from person to person. It seems to have something to do with neurotransmitters, and the receptors they bind to, and how they work to regulate each other. But testing for that would require knowing what the baseline is for that particular patient, and getting a sample would require a brain biopsy to examine local neurotrasmitter quantities as well as the density of their respective receptors. And we don’t know from where to take the biopsy and getting enough information may mean we would need to take several. And taking brain biopsies mean you cause local brain damage.
Functional MRI could be a non-invasive tool for determining overall brain metabolism in different functional areas and may eventually lead to more clues about what is wrong in the function of a depressed brain, possibly leading to diagnostic tests and personalized treatment opportunities, but we are a long way from that.
That is my understanding, as a medical doctor.
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