Symptoms of low serotonin may include mood changes, feelings of depression or anxiety, and difficulty with functions such as sleep and memory. Physical signs may include gastrointestinal symptoms or movement issues.

Serotonin is an essential hormone and neurotransmitter. It plays a role in a wide range of bodily functions, including sleep, appetite, mood, and thinking, but symptoms of a deficiency may be hard to spot.

The serotonergic system is highly complex, and scientists do not know precisely how it works. However, research links serotonin deficiency with conditions such as depression.

A better understanding of serotonin functioning may eventually lead to treatments for various conditions linked to low serotonin levels. However, for now, blood serotonin levels are not usually a reliable indicator of any specific disease.

This article explains what a person may notice if serotonin levels are low, why it happens, and how to address it.

A note about sex and gender

Sex and gender exist on spectrums. This article will use the terms “male,” “female,” or both to refer to sex assigned at birth. Click here to learn more.

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Serotonin is a hormone that the body naturally produces. Serotonin deficiency occurs when a person does not have enough of this hormone, which may affect various bodily functions.

Much remains unknown about serotonin and how it works. However, research links low serotonin activity with a range of mental health conditions, including:

Understanding serotonin

The central nervous system (CNS) produces and stores serotonin. The body uses an amino acid called tryptophan to produce serotonin.

Serotonin is a neurotransmitter that helps transmit messages in the CNS. However, it also contributes to the following functions:

Serotonin syndrome

Serotonin syndrome, also called serotonin toxicity, can occur if too much serotonin is active in the nervous system. This is a life threatening condition that may result from medication use, the use of recreational drugs, or drug interactions.

Symptoms include:

A person with serotonin syndrome needs immediate emergency medical help.

Serotonin helps regulate a wide range of bodily functions. However, since its role in the body is part of a complex process, it can be challenging to determine whether low serotonin or something else is causing a specific symptom.

The sections below explain some possible symptoms of low serotonin levels.

Psychological symptoms

Research links certain mental health symptoms with low serotonin activity, including:

  • Mood changes: Serotonin helps regulate mood. People who feel unusually irritable or down for no apparent reason may have low serotonin activity.
  • Depression: Feelings of sadness, hopelessness, and anger, as well as chronic fatigue and thoughts of suicide, may indicate depression.
  • Anxiety: A person with anxiety may worry excessively about specific issues or experience non-specific feelings of anxiety.
  • Dementia symptoms: Changes in certain serotonin receptors may contribute to behavioral and psychological symptoms of dementia, such as agitation, aggression, and apathy.
  • Sleep irregularities: Serotonin helps regulate sleep. Sleep problems may occur when there is an imbalance of serotonin.
  • Sexual function: Serotonin appears to affect sexual function. Medications that affect serotonin levels can have a complex effect on sexual function and drive.

In time, researchers may discover other ways low serotonin activity affects mental health.

Learn more about serotonin deficiency.

Suicide prevention

If you know someone at immediate risk of self-harm, suicide, or hurting another person:

  • Ask the tough question: “Are you considering suicide?”
  • Listen to the person without judgment.
  • Call 911 or the local emergency number, or text TALK to 741741 to communicate with a trained crisis counselor.
  • Stay with the person until professional help arrives.
  • Try to remove any weapons, medications, or other potentially harmful objects if it’s safe to do so.

If you or someone you know is having thoughts of suicide, a prevention hotline can help. The 988 Suicide and Crisis Lifeline is available 24 hours a day at 988. During a crisis, people who are hard of hearing can use their preferred relay service or dial 711 then 988.

Find more links and local resources.

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Role in physical health and possible symptoms

Serotonin may play a role in the nervous system. As such, it will affect the overall functioning of the body and may cause the following symptoms:

  • Gastrointestinal (GI) symptoms: Due to its role in the GI tract, changes in serotonin levels may lead to GI symptoms, including changes in appetite and bowel function.
  • Pain perception: Some people who experience psychological distress may have physical symptoms, such as chronic pain, with no apparent physical origin. A 2019 study suggests that disruptions in the serotonin pathway may contribute.
  • Movement issues: Some research suggests boosting serotonin activity may help reduce resting tremors in Parkinson’s disease, suggesting low serotonin activity may play a role in worsening symptoms.
  • Blood clotting: Serotonin plays a role in blood clotting. A 2021 article associates high serotonin activity with blood clotting. However, further research is necessary to understand the processes involved.
  • Wound healing: Some evidence suggests that serotonin plays a role in wound healing by increasing cell migration to areas needing regeneration. More research is necessary to know if low serotonin levels affect the body’s healing ability.
  • Bone density: Some mouse studies have suggested that low serotonin activity in some parts of the body may increase the risk of low bone density. However, more research is necessary to see if this applies to humans.
  • Pain: Various neurotransmitters, including serotonin, play a role in pain perception. Research associates problems with the serotonergic system with painful conditions, such as irritable bowel syndrome (IBS) and fibromyalgia.

Learn about mild serotonin syndrome.

Doctors may diagnose low serotonin based on a person’s symptoms, not blood serotonin levels.

However, they may recommend a test to measure serotonin levels if they suspect a carcinoid tumor. These tumors start in certain body cells and can appear in the lungs, stomach, small intestine, rectum, and appendix.

A doctor may test for a substance called 5-hydroxy indoleacetic acid (5-HIAA) if they suspect someone has a carcinoid tumor. When serotonin undergoes oxidative reactions, 5-HIAA forms, and the body eliminates it in urine.

Learn more about carcinoid syndrome.

A doctor may prescribe medications or suggest lifestyle changes to help someone maintain their serotonin levels.


Medications can boost serotonin activity. These drugs include the following antidepressants:

They work in different ways. According to the UK’s National Health Service (NHS), doctors prescribe SSRIs and SNRIs more often than the older style MAOIs, which can have adverse effects.

Learn how to increase serotonin levels with and without medication.

Lifestyle changes

Doctors may suggest certain lifestyle changes or non-medicinal treatments for people with symptoms of low serotonin, such as:

  • Psychotherapy: Psychotherapy may improve the symptoms of various mental health conditions, including anxiety and depression.
  • Manage stress: Chronic stress may affect how the brain processes or produces serotonin and may lead to a wide range of symptoms, such as mood changes. Managing stress may help keep serotonin neurotransmission stable, and this may help regulate mood.
  • Light therapy: A doctor may suggest light therapy to help with mental health problems such as seasonal affective disorder (SAD). This may boost serotonin production and improve mood.
  • Exercise: Research suggests exercise can help raise serotonin levels, boost mood, and manage depression.
  • Dietary changes: Some research suggests that various dietary nutrients could help boost serotonin levels, including foods containing the amino acid tryptophan.

More about lifestyle changes to balance serotonin levels

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Serotonin function may vary between males and females.

Estrogen, which is higher in females, can affect the production, use, and degradation of serotonin. According to a 2019 review, animal studies suggest that boosting estrogen levels may lead to an increase in serotonin.

However, it may depend on how long estrogen treatment lasts. In one study, serotonin levels fell as estrogen therapy progressed.

Learn more about estrogen in males and females.

Serotonin plays a role in many aspects of health, and a deficiency could occur, leading to a wide range of medical conditions.

Moreover, not everyone with symptoms of depression or other mental health conditions will have low serotonin. Symptoms alone will not show if a person has low serotonin activity.

A person should see a doctor for the following reasons:

  • feelings of sadness or anxiety that do not improve with self-care
  • memory loss
  • movement issues
  • changes in sleep, appetite, or digestion
  • any side effects due to serotonin-related treatments
  • signs of serotonin toxicity, especially after taking prescription or recreational drugs

How does someone know if they have serotonin deficiency?

It is not possible for an individual to know if their serotonin levels are low. However, people who see a doctor with persistent symptoms of depression may benefit from medication and lifestyle measures that regulate serotonin function.

How can someone fix serotonin deficiency?

Medications, such as SSRIs or SNRIs or lifestyle changes can help people boost their serotonin levels. A healthcare professional may suggest regular exercise, dietary changes, and stress management.

Does low serotonin cause anxiety?

Research associates low serotonin activity with certain mental health conditions, such as anxiety disorders. However, other factors, including trauma, medications, and childhood experiences, may also cause anxiety.

Serotonin contributes to a wide range of bodily functions, and many aspects of well-being may depend on a balance in serotonin activity. Low serotonin levels may have links to certain mental health issues.

However, measuring serotonin levels is not usually how doctors diagnose a health condition. A doctor will likely focus on a person’s symptoms, carry out other tests, and then treat the condition they diagnose.

Some conditions may respond well to treatments that boost serotonin activity in the body, such as SSRIs, SNRIs, or lifestyle changes, including regular exercise and dietary changes.