A paper was recently published that reviews the serotonin theory of depression. Media articles have been presenting the findings of this study in a confusing manner, implying that the findings of this paper mean that depression should not be treated with antidepressants. This misunderstanding is because drug companies often present depression in an overly simplistic manner as being caused by low serotonin levels. The paper, by Moncrieff et al. entitled “The Serotonin theory of depression: a systematic umbrella review of the evidence”, makes the case that low serotonin level is likely not the direct cause of depression.  The research presented in the paper was not about antidepressant medications nor their efficacy.

Psychiatrists and psychologists, and researchers in neuroscience, have long known that the cause of depression is not easy to pin down, and the serotonin hypothesis has been (successfully) called into question many times over the years.  An easy way of glimpsing the complexity of depression is looking at the drugs which treat it: some affect serotonin, yes, but others have no serotonin action at all.  Some, like bupropion, affect norepinephrine and dopamine.  Some, like lithium and lamotrigine, do not directly affect any of these three neurotransmitters.  And all of them work in a large percent of patients.  To mental health professionals, this paper about serotonin is not nearly as groundbreaking as is being presented by newspapers and magazines. 

Like most medical conditions, particularly in the brain, depression is complicated and there are many different factors which cause and contribute to the suffering of people with mood disorders.  The paper by Moncrieff et al did not address the efficacy of antidepressants in any way; drugs are not prescribed because of theories of why they should work, they are prescribed after it is proven that they do work in rigorous blinded clinical trials.  

In sum:  A paper indicating that brains of depressed patients are not low in serotonin does not mean that antidepressants don’t work.

This article from Vice does a great job at laying out the set of complicated points of view: The New Study on Serotonin and Depression Isn’t About Antidepressants

We also recommend this article from The Guardian: The chemical imbalance theory of depression is dead – but that doesn’t mean antidepressants don’t work