Antidepressants do something, but that is not evidence that they work. A recent study showed that the evidence they manage depression is bunk and that doctors don't really understand what causes depression, but it is not a "chemical imbalance."

From what I recall, they created chemical imbalances of the substances SSRIs affect in lab rats and they did not show or develop signs of depression. I think they did this is volunteer humans as well by adjusting their diet to create chemical imbalances (and measurement) and found happy people remained happy, depressed people remained depressed. Thus the study concluded that SSRIs affecting serotonin are not doing what psychiatrists think they are doing.