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# Serotonin

ser·o·to·nin - ser-uh-TOE-nin

## Definition

Serotonin is a neurotransmitter and [hormone](/glossary/hormone) that plays a wide-ranging role in regulating mood, sleep, appetite, digestion, pain perception, and cognitive functions including memory and learning. It's often called the "happiness" [neurotransmitter](/glossary/neurotransmitter) because of its association with feelings of wellbeing and contentment, though its functions extend far beyond mood regulation.

Remarkably, approximately 90% of the body's serotonin is produced not in the brain but in the gastrointestinal tract, where it helps regulate intestinal movements, appetite, and nausea. The serotonin produced in the brain - while a small fraction of total body serotonin - has profound effects on mood, anxiety, sleep, and social behavior. The brain produces serotonin from tryptophan, an essential [amino acid](/glossary/amino-acid) obtained from food.

Serotonin's role in mental health is the basis for the most widely prescribed class of antidepressants: selective serotonin reuptake inhibitors (SSRIs) like fluoxetine (Prozac), sertraline (Zoloft), and escitalopram (Lexapro). These medications work by preventing the reabsorption of serotonin in the brain, effectively increasing the amount available for signaling between neurons.

## Also Known As

5-HT 5-hydroxytryptamine 

## Key Facts

-   • About 90% of serotonin is found in the gut, not the brain. 
-   • Serotonin is synthesized from the amino acid tryptophan, found in foods like turkey, eggs, nuts, and cheese. 
-   • SSRIs - the most commonly prescribed antidepressants - work by increasing serotonin availability in the brain. 
-   • Serotonin helps regulate the sleep-wake cycle through its role as a precursor to melatonin (the sleep hormone). 
-   • Low serotonin levels are associated with depression, anxiety, insomnia, and irritability. 
-   • Sunlight exposure stimulates serotonin production - which may explain seasonal patterns of depression (SAD). 

## How It Relates To Your Health

Serotonin is relevant to anyone interested in understanding mood, sleep, and digestive health. If you've been prescribed an SSRI or discussed depression and anxiety with a healthcare provider, understanding serotonin helps you appreciate how these medications work and why the gut-brain connection matters for mental health.

Natural strategies that support serotonin production include regular exposure to bright light (especially morning sunlight), exercise, a diet rich in tryptophan-containing foods, adequate sleep, and maintaining a healthy [gut microbiome](/glossary/microbiome). These approaches complement - but do not replace - medical treatment for mood disorders.

## Related Terms

[Dopamine](/glossary/dopamine)[Cortisol](/glossary/cortisol)[Microbiome](/glossary/microbiome)[Blood-Brain Barrier](/glossary/blood-brain-barrier)

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## Sources

1.  [Serotonin](https://my.clevelandclinic.org/health/articles/22572-serotonin) - Cleveland Clinic
2.  [Serotonin: What It Is, How to Increase It](https://www.healthline.com/health/mental-health/serotonin) - Healthline (medically reviewed)
3.  [Physiology, Serotonin](https://www.ncbi.nlm.nih.gov/books/NBK545168/) - StatPearls / PubMed

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