Adam Hadhazy writes in Think Twice: How the Gut's "Second Brain" Influences Mood and Well-Being:

The enteric nervous system uses more than 30 neurotransmitters, just like the brain, and in fact 95 percent of the body's serotonin is found in the bowels.

Is that claim true? Is the majority of serotonin that's used by the body found in the bowels and not in the brain?

  • A semi-popular phrase in emerging science these days is "gut-brain connection". You might find lots of information from just a google of that phrase.
    – user11643
    Jun 3, 2019 at 3:42

1 Answer 1


According to Serotonin in the Gastrointestinal Tract Current Opinion in Endocrinology, Diabetes and Obsesity (2009) volume 16, pages 53-59:

95% of the serotonin in the body is located in the gut

Furthermore, this does not mean the rest is in the brain. Serotonin is also in platelets. There is a nice explanation in Relationship of Platelet Serotonin to Disturbances of Clotting and Hemostasis Circulation 1957; 15:353-357

Janewayand coworkers found that platelets were essential to the vasoconstrictor activity of serum. This observation was later confirmed by several other investigators. In 1948, a crystalline vasoconstrictor substance was isolated from serum by Rapport and associates and named "serotonin." This substance, subsequently identified as 5-hydroxytryptamine, is derived biologically from tryptophan. [references omitted]

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