The whole chemical imbalance idea is not so far off it's just that there is no test available to be able to tell which chemical or chemicals are out of balance.
Unfortunately the big pharms and doctors too have been so stuck on the serotonin bit that they have done more damage to people than help.
Try being mildly Bipolar and not knowing it and get put on a SSRI or SNRI see what happens. That is not a pretty picture at all.
