Neurotransmitter function seems to be normal in people with mental illness before treatment. In Whitaker's words:Prior to treatment, patients diagnosed with schizophrenia, depression, and other psychiatric disorders do not suffer from any known "chemical imbalance." However, once a person is put on a psychiatric medication, which, in one manner or another, throws a wrench into the usual mechanics of a neuronal pathway, his or her brain begins to function…abnormally.Carlat refers to the chemical imbalance theory as a "myth" (which he calls "convenient" because it destigmatizes mental illness), and Kirsch, whose book focuses on depression, sums up this way: "It now seems beyond question that the traditional account of depression as a chemical imbalance in the brain is simply wrong."
Read the whole thing, and don't let anyone you know start taking those drugs. Future generations will probably look at these things the way we look at the doctors who treated people by bleeding them.