Serotonin: Where It’s Produced, Its Function, and Symptoms of Low and High Levels


Serotonin, also known as 5-hydroxytryptamine (5-HT), is a chemical messenger that plays a vital role in the body. It acts as both a neurotransmitter and a hormone, facilitating communication between nerve cells and regulating various physiological processes. This article explores the production sites of serotonin, its functions, and the symptoms associated with both low and high levels. Understanding the role of of this hormone in the body can provide valuable insights into its impact on physical and mental well-being.

Where is Serotonin Produced?

The Complex Process of Serotonin Production: 

Serotonin production begins with the conversion of tryptophan, an essential amino acid obtained through dietary sources. 

  • Approximately 10% of serotonin is synthesized in the brain, mainly originating from neurons in the raphe nuclei located in the brainstem. These neurons form an extensive network projecting throughout the brain, ensuring widespread distribution and crucial functions.
  • The Role of the Intestine: Surprisingly, around 95% of serotonin is synthesized in the intestine. Specialized cells lining the intestines contribute significantly to production. Intestinal serotonin functions as a hormone, exerting autocrine, paracrine, and endocrine effects. It regulates gut motility, digestive function, and interacts with the gut microbiota. Additionally, it can travel through the bloodstream to target tissues and organs, influencing physiological processes beyond the digestive system.
Structure of serotonin
Structure of serotonin

Function of Serotonin

1. Mood Regulation: 

Serotonin, often referred to as the “happy” chemical, plays a crucial role in mood regulation. It affects feelings of happiness and well-being, and low levels can be associated with depression. Medications targeting this hormone are commonly used in treating mood disorders.

2. Sleep and Wakefulness: 

Serotonin is involved in the regulation of sleep patterns. It helps switch between REM and non-REM sleep stages and influences the timing of the circadian rhythm. It also serves as a precursor to melatonin, a hormone that regulates sleep.

3. Bowel Movements and Digestion: 

Serotonin produced in the intestines controls bowel movements and contributes to the overall functioning of the digestive system.

4. Blood Clotting: 

Platelets store and release it to aid in blood clotting, promoting the clotting process when the body needs to repair damage.

5. Nausea:

In the stomach and intestines it can stimulate nausea and vomiting in response to certain foods, illness, or other conditions.

6. Bone Metabolism: 

Serotonin’s role in bone health is complex. Circulating levels (hormonal form) have been associated with reduced bone density, while the hormone in the brain contributes to bone tissue formation and maintenance.

7. Sexual Function: 

Serotonin influences sexual function, with high levels potentially decreasing libido and low levels potentially increasing it. Medications affecting the levels can have sexual side effects.

8. Learning, Memory, and Executive Function:

 Serotonin receptors in the brain are involved in cognitive processes such as learning, memory, and executive functions. Low levels may contribute to difficulties in these areas.

9. Mental Health: 

Serotonin is implicated in various mental health disorders, including depression, anxiety disorders, OCD, PTSD, phobias, and epilepsy. Medications targeting this hormone or its receptors are commonly used for treatment.

10. Other Potential Functions: 

Serotonin’s role is still being explored in areas such as cardiovascular health, eye health, neurological disorders, appetite regulation, and gut disorders like IBS. Further research is needed to fully understand these relationships.

Serotonin physiology
Serotonin physiology

Symptoms of Low Serotonin Levels 

Low levels can lead to several physical and mental symptoms, including:

  1. Mood disturbances: Persistent feelings of sadness, low mood, irritability, anxiety, or mood swings.
  2. Sleep disturbances: Difficulty falling asleep, staying asleep, or poor sleep quality, resulting in fatigue and lethargy.
  3. Changes in appetite and weight: Decreased appetite leading to unintended weight loss or increased cravings for carbohydrates and comfort foods, leading to weight gain.
  4. Digestive issues: Digestive problems such as IBS, constipation, diarrhea, abdominal pain, or bloating.
  5. Reduced libido: Decreased sexual desire or sexual dysfunction.
  6. Fatigue and low energy: Feelings of fatigue, low energy, and a lack of motivation or drive.

Symptoms of High Serotonin Levels

High serotonin levels can cause serotonin syndrome, which may manifest in the following symptoms:

  1. Agitation and restlessness
  2. Confusion and disorientation
  3. Rapid heart rate and elevated blood pressure
  4. Dilated pupils
  5. Sweating and shivering
  6. Tremors and muscle rigidity
  7. Gastrointestinal issues
  8. Headache Severe cases of serotonin syndrome can lead to life-threatening complications, including seizures, high fever, irregular heartbeat, unconsciousness, and organ failure.

Regulating Serotonin: Treating Low and High Level

Treating Low level:

  • Medications: SSRIs improve its usage and are commonly prescribed for depression symptoms. Depending on symptom severity and duration, long-term SSRI use may be necessary.
  • Dietary supplements: SAMe aids the hormone synthesis, while 5-HTP boosts hormone levels. Probiotics increase tryptophan, aiding its production.
  • Natural methods: Increase tryptophan intake through foods like eggs, tofu, salmon, turkey, nuts, seeds, and cheese. Combining high-tryptophan foods with carbohydrates enhances brain access. Sunlight or light therapy improves its levels. Regular exercise releases tryptophan and promotes production. Massage therapy and meditation elevate serotonin levels.

Treating High level:

  • Adjusting or stopping medications: Discontinue or modify medication dosage for mild serotonin syndrome cases caused by medication.
  • Hospital medications: Prescribe benzodiazepines to reduce agitation, seizures, and muscle stiffness. Periactin blocks serotonin production.
  • Hospitalization and monitoring: Severe serotonin syndrome cases require close monitoring during extended hospital stays. Muscle paralysis medications and breathing machines may be used to prevent damage.

Consult a healthcare provider before starting new supplements or treatments to receive personalized recommendations and ensure safety regarding potential risks or interactions.


Serotonin, as a neurotransmitter and hormone, plays a critical role in the body’s physiological and psychological processes. Understanding its production sites, functions, and the symptoms associated with low and high levels can provide valuable insights into its impact on overall well-being. While deficiency and excess can lead to various symptoms, it is essential to consult with a healthcare professional for accurate diagnosis and appropriate treatment. Ongoing research continues to expand our understanding of it’s intricate mechanisms and its role in different aspects of health.

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Binod G C

I'm Binod G C (MSc), a PhD candidate in cell and molecular biology who works as a biology educator and enjoys scientific blogging. My proclivity for blogging is intended to make notes and study materials more accessible to students.

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