Gut Bacteria and Depression: Harvard Finds the Missing Inflammation Link

# Gut Bacteria and Depression: Harvard Finds the Missing Inflammation Link

> **Quick answer:** Harvard Medical School researchers have identified a specific mechanism by which gut bacteria may cause depression: a common bacterium called *Morganella morganii*, when exposed to an industrial chemical found in personal care products, produces a modified molecule that triggers the immune system to release interleukin-6 (IL-6) — an inflammatory protein strongly linked to major depressive disorder. The finding, published in the Journal of the American Chemical Society, suggests that some cases of depression may originate not in the brain but in the gut, and could be treated like an autoinflammatory condition.

*This article is for informational purposes only and does not replace professional medical advice. Consult a healthcare provider for medical concerns.*

Depression is one of the most diagnosed and least understood conditions in medicine. We know serotonin is involved. We know stress is a trigger. But for millions of people, antidepressants barely work — and researchers have never been able to fully explain why. A January 2025 study from Harvard Medical School may have just revealed a missing piece: **gut bacteria and the inflammation they produce when exposed to everyday chemicals.**

## What Harvard Scientists Actually Found

The study, published in the *Journal of the American Chemical Society* and led by senior author Jon Clardy — Christopher T. Walsh Professor of Biological Chemistry at Harvard Medical School — focused on a bacterium called *Morganella morganii* (*M. morganii*). Multiple previous studies had already linked *M. morganii* to depression and inflammatory conditions including type 2 diabetes and inflammatory bowel disease. But no one had explained the molecular "how."