"Scientifically speaking, there never was a network of validated hypotheses capable of sustaining a full-blown, global chemical imbalance theory of mental illness. Moreover-and here we come back to Myth 2-psychiatry as a profession and medical specialty never endorsed such a bogus “theory,” when judged by its professional organizations, its peer-reviewed publications, its standard textbooks, or its official pronouncements."

https://www.psychiatrictimes.com/view/debunking-two-chemical...

In the general public, there's a logical fallacy that people seem to fall for when thinking about psychopharmacology. It seems that when it is learned that serotonin re-uptake inhibitors (SSRIs)are used to treat patients with depression it is followed with some mechanistic explanation of a "chemical imbalance" resulting from "not enough serotonin."

Yet people don't make this mistake when talking about opiods or pain killers. If you break your arm and the doctor prescribes Codeine we don't come to the conclusion that "you broke your arm and all your endogenous opoids came spilling out so we had to replace it with Codeine." Although Tylenol/paracetamol are useful for treating pain, we don't hear a lot of talk about Tylenol deficiencies.