The medical profession has often embraced unscientific theories when dealing with mental illness. Some of their treatments have worked and some haven’t that is true of medicine in general but their theories have a tendency to be simply unbelievable.
Take Freudian psychoanalytic theory which is comprised a lot of entities and processes that are like just-so stories. I was there in the 50s; I had a young open mind; and I tried to take it seriously but failed. It was just not believable. Many ordinary people I knew felt the same. There was no evidence that the brain worked in that way no experiments, no statistical tests, only interpretations of individual cases. Some patients found psychoanalysis helpful but there was no proof that other ‘talk’ methods were not better and no evidence that the talk’s success, when it was successful, was connected to the theory.
Now we have another silly theory, chemical imbalance. This time we assume that the brain is something like a vat of chemicals; illness is too much or too little of some particular chemical; and the condition can be corrected by adding or subtracting that chemical. The medicines work somewhat some of the time, but usually their testing leaves a lot to be desired. We do not know if they ever even reach the brain, and we do not know what they do if they get there. The whole theory is based on assumptions. Biochemistry is complex and effects are not straightforward and a lot of effects are counterintuitive.
Where is the science behind the theory? Neuroscience is slowly building a picture of how the brain works and so far it has all most nothing in common with either the Freudian scheme or imbalance of chemicals in a ‘vat’. Those theories are simply fairy stories made out of whole cloth. That does not mean that there are no correlations or effective treatments just that a better theory is needed than chemical imbalance.