If low serotonin levels aren’t responsible for depression, what is?

http://www.theguardian.com/science/blog/2010/sep/28/depression-serotonin-neurogenesis

If low serotonin levels were responsible for depressed mood, then we should be able to induce depression in people by decreasing serotonin, and we should find low levels of serotonin in patients with depression. But neither of those things exist. Decreasing serotonin in humans can lower your mood, but it doesn’t always work. And studies looking for low serotonin in depressed patients have been inconclusive. It appears that even though antidepressants increase serotonin, a lack of serotonin doesn’t cause depression (kind of like aspirin treats a headache, but headaches are not caused by a lack of aspirin)…

http://psychcentral.com/news/2015/02/18/low-serotonin-depression-theory-challenged/81396.html

A new paper challenges the prevailing opinion that depression is related to low levels of serotonin in the gaps between nerve cells in the brain. This theory has predominated for nearly 50 years and has led to the development of the commonly prescribed anti-depressant medications called selective serotonin re-uptake inhibitors, or SSRIs. But it has never been proven…

“It’s time we rethink what we are doing,” Andrews says. “We are taking people who are suffering from the most common forms of depression, and instead of helping them, it appears we are putting an obstacle in their path to recovery.”

When depressed patients on SSRI medication do show improvement, it appears that their brains are actually overcoming the effects of antidepressant medications, rather than being assisted directly by them. Instead of helping, the medications appear to be interfering with the brain’s own mechanisms of recovery…

Andrews, an evolutionary psychologist, has argued in previous research that antidepressants leave patients in worse shape after they stop using them, and that most forms of depression, though painful, are natural and beneficial adaptations to stress.