Common mental disorders like depression are most likely not the result of chemical imbalances. This is not, however, an indictment of biopsychiatry.
Biopsychiatry -- not without a nod and a wink from Big Pharma -- has oversold itself in the last 15-or-so years by making overgeneralized and oversimplified statements about so-called "chemical imbalances". That's far from the actual, more complex and realistic, claims of scientific biopsychiatry.
Actually, post-
Prozac mainstream
biological psychiatry tends to maintain that
depression is about the death of neurons in your "
mammalian brain", so to speak.
SSRIs like Prozac (which make your brain marinate in its available serotonin longer) don't work until a few weeks after beginning treatment, even though serotonin levels are immediately shot up. That is, SSRIs are stimulating neuron regrowth (yes, it's been observed in controlled lab settings).
More strongly, dr. Post's 1980 observation of the kindling phenomenon in bipolar disorder has led him to link manic-depressive illness to epilepsy -- which is why most drugs for epilepsy have either been approved or used extensively on an off-label basis in bipolar disorder. Most recently drug companies have seeked approval of atypical antipsychotics for bipolar disorder and academia has come up with an alternative, gene-based theory I don't really understand but which brings "chemical imbalances" back into the debate. Of course, the attentive between us have noticed that this alternate development has come exactly when the main anticonvulsants went generic, that is, lost their patents, so any smaller pharmaceutical company can make lamotrigine, topiramate, etc. You don't spend your shareholder dollars pushing Lamictal when cheaply available equivalents like Indian-produced Lamitor can be found.
As someone who suffers from bipolar disorder, I'm fond of the (older) convulsive hypothesis for bipolar disorder; temporal lobe epilepsy shares quite a few symptoms with us, and I'd very much like to be able to tell my boss that I have a form of epilepsy than keep the bald-faced lie that I suffer from strong, disabilitating fits of the migraines. So I'm not impartial on this. But I have deep suspicions that epilepsy, migraine and bipolar disorders are Three Buzzing Conditions
(Actually, some of the anticonvulsants we guys at bipolar disorder share have also been approved for migraines or only for migraines (like Topamax). For the longest while, until I was put on Seroquel as an add-on, I could credibly claim that all the drugs I was taking (Lamictal, Depakote, Topamax) were meant for those disabilitating migraines I don't have. Migraines can be detected in imaging tests as stronger blood vessal pressure, but the "reverse" evidence from drug efficacy suggests that electrical convulsions are behind the buzzing three conditions -- epilepsy, bipolar disorder and migraines.)