The serotonin story: what the evidence said, and what patients were told

Almost everyone prescribed an antidepressant in the last thirty years has heard some version of it: depression is caused by a chemical imbalance, the imbalance involves serotonin, and the medication corrects it. Often it was said kindly, to lift a weight of self-blame. What happened underneath is that the research moved on and the sentence did not. This is about that gap - not about whether antidepressants work, which is a different question with different evidence.

Significant findings

A pre-registered umbrella review in Molecular Psychiatry covered six areas of serotonin research across seventeen studies and concluded that they "provide no consistent evidence of there being an association between serotonin and depression, and no support for the hypothesis that depression is caused by lowered serotonin activity or concentrations." Two meta-analyses of the metabolite 5-HIAA showed no association with depression, and a meta-analysis of plasma serotonin found lowered concentrations associated with antidepressant use rather than with depression. The two largest studies of the serotonin transporter gene, covering 115,257 and 43,165 people, found no association with depression and none of the gene-environment interaction that had been one of psychiatry's most cited findings.

That review was contested in print, and the rebuttal belongs on the same page. Jauhar and colleagues responded in the same journal: "We present reasons for why this conclusion is overstated, including methodological weaknesses in the review process, selective reporting of data, over-simplification, and errors in the interpretation of neuropsychopharmacological findings."

The gap was noticed early: Lacasse and Leo published an analysis in PLoS Medicine in 2005, seventeen years before the umbrella review, of the distance between what SSRI advertising claimed and what the literature supported - while that advertising was still running.

The right word for this is not "lie". That claims knowledge of intent, which is exactly what cannot be documented from outside. A story that outlived its evidence is the accurate description: a hypothesis became a shorthand, the shorthand was genuinely useful because it moved depression from character defect to medical condition, advertising had every reason to keep it simple, and it stayed in circulation long after the research beneath it stopped supporting it. Nobody had to lie for that to happen.

None of this tells you your medication is doing nothing. Whether a drug helps and why it helps are separate questions answered by separate evidence - aspirin was in use for roughly seventy years before prostaglandins were understood, and lithium's mechanism is still unsettled. On the outcome, a network meta-analysis of 21 antidepressants in The Lancet found them more effective than placebo for adults with major depressive disorder. Both are true at once; they answer different questions.

What it changes is not the pharmacology but informed consent and self-understanding. If you agreed to a medication because you were told it corrects a deficiency, you agreed on a footing the research does not clearly support. And "you have a chemical imbalance" is a story about a broken part - so when treatment only partly helps, that story quietly implies a broken person.

Worth asking

When you say this medication helps, what outcome are we expecting, and by when? What is the evidence that it helps my situation, separate from the explanation of how? If it only partly helps, what is the next option? And if I ever want to stop, what taper and check-ins would you want in place first? Nothing here is a reason to stop: a randomised trial in UK primary care found 56% of those randomised to discontinue relapsed within a year against 39% who continued, and stopping abruptly can be dangerous. Stop deliberately, with a prescriber and a plan, if you stop at all.