If I recall, this theory came out of Eli
Lilly when it came out with Prozac, and it was reinforced by a book by a psychiatrist paid by
Eli Lilly that became a best seller when that drug was the first SSRI to come out. They claimed, and the book claimed even more, that this was the end of mental illness, which of course was and is ridiculous and we now know that serotonin levels may have nothing to do with why a person starts to have mental problems.