Most of Your Serotonin Is Made in the Gut

About 90% of the body’s serotonin is made in the gut, where it helps digestion and can communicate with the brain through the gut-brain axis.

Biology

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Serotonin is often thought of mainly as a brain chemical, but most of the body’s serotonin is actually produced in the gastrointestinal tract. Specialized intestinal cells called enterochromaffin cells make roughly 90% to 95% of the body’s serotonin, while the brain produces its own supply. In the gut, serotonin helps control processes such as movement of the intestines, secretion, and interactions with the immune system. Gut microbes can also influence serotonin production and metabolism, making the gut microbiome part of a much larger communication network between the digestive system and the nervous system. The important distinction is that serotonin made in the gut does not simply travel through the blood and enter the brain because it cannot cross the blood-brain barrier in that way. Instead, researchers are studying several indirect routes through which gut activity may communicate with the brain, including nerve signals, immune signals, hormones, and microbial products. This gut-brain connection is an active area of research, with possible relevance to digestion, inflammation, mood, and neurological conditions, but the mechanisms are complex and many proposed links are still being investigated. The basic fact is striking on its own: the overwhelming majority of the body’s serotonin is associated with the gut rather than being produced in the brain.

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