There's an interesting article on the CNCNews website discussing the lack of scientific research behind the chemical imbalance model for explaining depression.
“And as early as 1998, the American Psychiatric Association in its textbook says we’re not finding that people with depression have any abnormality in their serotonin, but because it’s such an effective metaphor for getting people to take the drugs and sell the drugs, it’s continued to be promoted.”
Not only are antidepressants not effective, but taking them may actually exacerbate symptoms of depression...
"while people suffering from depression may not have low serotonin levels to begin with, the use of SSRIs reduces the brain’s capacity to produce serotonin on its own, leading to a worsening of symptoms when patients stop taking the drugs."
An interesting read indeed.