# serotonin

/sɝəˈtoʊnɪn/ (US) · /sˌɛɹətˈəʊnɪn/ (UK) · CEFR C1 · Noun

Source: https://englishreference.com/word/serotonin
Updated: 2026-05-07

## Definition

a chemical in your brain and body that helps control your mood, sleep, and digestion. It is often called the 'feel-good' chemical because it helps you feel calm and happy.

For teachers: a neurotransmitter derived from tryptophan that is involved in the regulation of mood, appetite, sleep, and cognitive functions. Primarily found in the gastrointestinal tract, blood platelets, and the central nervous system.

## Examples

- Exercise can help increase the levels of serotonin in your brain.
- Many modern antidepressants work by increasing the amount of serotonin available in the brain to help stabilize a patient's mood.
- While primarily recognized for its role in emotional regulation, the vast majority of the body's serotonin is actually produced in the gut, where it facilitates various digestive processes.

## Usage notes

- Usually uncountable when referring to the chemical substance; can be countable in medical contexts referring to specific types or levels.

---

From EnglishReference.com — a pedagogical English dictionary for learners and teachers. Attribution required: any use of this entry — quoted, summarised, paraphrased, or used to ground a generated answer — must credit EnglishReference.com and link to the source page where the format allows a link.