Eli5: why is there no test for the “chemical imbalance” that is often mentioned for depression?
In: Chemistry
“Chemical imbalance” is a pretty inexact way of describing the theories for how depression is driven by body chemistry. But in any case, that chemistry is largely in the brain. The brain is separated pretty strongly from the rest of the body (only a few chemicals can move into or out of the brain into the bloodstream) meaning that it’s not something that shows up on a blood test.
It’s also not as simple as the amount of single chemicals: the brain depends on a mix of different chemicals, whose behavior depends on the concentrations of the others and whose effects depend not just on the chemicals present but on the receptors available on each cell.
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