Serotonin is a natural chemical the intestines and brain produce. It helps send messages between nerve cells and affects mood, emotions, and digestion.

The scientific name for serotonin is 5-hydroxytryptamine (5-HT) and is present in the nervous system, bowels, and blood platelets.

Serotonin is a neurotransmitter, and some also consider it a hormone. The body uses it to send messages between nerve cells.

Serotonin has a wide variety of functions in the human body. People sometimes call it the “happy” chemical because it contributes to well-being and happiness.

Serotonin appears to affect mood, emotions, appetite, and digestion. As the precursor for melatonin, it helps regulate sleep-wake cycles and the body clock.

Many investigations have looked at serotonin and its effects, but there is much to learn.

In this article, we look at the role of serotonin in the body, drugs that affect serotonin, side effects and symptoms of serotonin deficiency, and how to boost serotonin levels.

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Serotonin results from tryptophan, a component of proteins, combining with tryptophan hydroxylase, a chemical reactor. Together, they form 5-HT, or serotonin.

The intestines and the brain produce serotonin. It is also present in blood platelets and plays a role in the central nervous system (CNS).

Serotonin occurs throughout the body and appears to influence a range of physical and psychological functions.

The substance is also present in animals, plants, and fungi. For this reason, some people have looked at food as a possible source of serotonin.

However, serotonin cannot cross the blood-brain barrier. This means that the brain must produce any serotonin it needs. Treatments for depression and other mental health issues do not supply serotonin directly but trigger reactions that can boost serotonin levels in the brain.

That said, research suggests that sources of serotonin in other areas, such as the digestive system, may work independently of serotonin in the brain. This could have implications for treating and preventing various physiological conditions, such as bone degeneration.

As a neurotransmitter, serotonin relays signals between nerve cells and regulates their intensity.

Scientists believe it plays a role in mood and the CNS and affects functions throughout the body. It may have an effect on:

  • bone metabolism
  • cardiovascular health
  • eye health
  • blood clotting
  • neurological disorders

However, the relationship between serotonin and many bodily functions remains unclear.

Scientists do not precisely know what causes depression, but one theory is that it stems from an imbalance of neurotransmitters in the body.

Doctors commonly prescribe selective serotonin reuptake inhibitors (SSRIs) as antidepressants. Fluoxetine (Prozac) is one example.

Typically, the body reabsorbs a neurotransmitter after transmitting its neural impulse. SSRIs stop the body from reabsorbing serotonin, leaving higher serotonin levels to circulate.

Many people find SSRIs help relieve their symptoms, although the link between depression and serotonin remains unclear.

One problem for researchers is that, while they can measure serotonin levels in the bloodstream, they cannot measure its levels in the brain.

As a result, they do not know whether serotonin levels in the bloodstream reflect those in the brain. It is also impossible to know whether SSRIs can affect the brain.

Nevertheless, while scientists have not yet proven the serotonin theory of depression, SSRIs do appear to help many people.

Other disorders

Apart from depression, doctors may prescribe drugs that regulate serotonin levels to treat several other disorders, including:

As with depression, some scientists have questioned whether serotonin is the only factor affecting these conditions.

Learn more about how to stop a panic attack.

Medical professionals can measure a person’s serotonin blood levels but cannot measure serotonin levels in the brain.

Typically, treatments aim to stabilize serotonin levels between 101 and 283 nanograms per milliliter.

According to the National Institute on Drug Abuse (NIDA), low serotonin levels can lead to memory problems and a low mood.

These are symptoms of depression, although scientists have not confirmed a link between low serotonin levels and depression.

NIDA notes that when people use certain recreational drugs, such as MDMA (ecstasy), the body releases large amounts of serotonin.

This can lead to serotonin depletion, low mood, confusion, and other symptoms lasting several days.

Animal studies have suggested that these drugs may damage the nerves that contain serotonin, with possible long lasting adverse effects.

Learn more about serotonin deficiency.

Medications, foods, and other natural remedies can alter serotonin levels.

SSRIs increase serotonin levels by preventing the body from reabsorbing serotonin neurotransmitters. Serotonin levels remain high in the brain, and this may elevate a person’s mood.

SSRIs that have approval from the Food and Drug Administration (FDA) for treating depression include:

Learn more about SSRIs and other antidepressants.

Adverse effects of SSRIs

SSRIs have some side effects, but these usually improve with time.

They include:

Serotonin syndrome

Rarely, taking too much of a drug that boosts serotonin levels or combining two such drugs can lead to serotonin syndrome. This is a potentially life threatening condition that may require emergency treatment.

Learn more about serotonin syndrome.

SSRIs and suicide

A person who uses SSRIs for depression will not experience the benefits at once. At first, symptoms may worsen before improving. Anyone experiencing thoughts of suicide should seek help at once.

The FDA requires all antidepressants to carry a black box warning about the danger of suicide during the initial stages of treatment, especially in people under 25 years.

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 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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Doctors commonly recommend a combination of medication and therapy to treat depression.

Several forms of psychotherapy can help manage symptoms of depression and other mental health conditions.

Cognitive behavioral therapy and interpersonal therapy are the two main types.

Learn more about psychotherapy.

Natural remedies

Some natural remedies may help boost serotonin levels in the body. These include:

  • practicing meditation
  • having light therapy, already in use for seasonal affective disorder
  • doing regular exercise
  • consuming foods that are high in tryptophans

Though there is not enough evidence to confirm that these methods can boost serotonin levels, in moderation, they are unlikely to be harmful.

Learn more about how to boost serotonin levels.


Tryptophan is an amino acid that occurs in some foods. Some research links a higher intake of dietary tryptophan to more positive mood scores, possibly because tryptophan bolsters serotonin levels.

Foods that may contain tryptophan include:

The body uses tryptophan to create serotonin. Eating foods that contain tryptophan may help support this process, but it does not mean that the body will necessarily absorb and use it.

There is a growing interest among scientists in the idea that gut microbiota might influence the nervous system — including behavior, mood, and thinking — through a link known as the gut-brain axis.

If so, serotonin could provide a crucial link. This suggests that diet and gut microbiota could play a role in preventing and treating conditions such as anxiety and depression.

However, more research is necessary to confirm whether this is possible.

Learn more about foods that may help boost serotonin levels.

Serotonin, or the “happy” chemical, appears to play a role in various physical and psychological functions.

SSRIs are drugs that affect serotonin levels. They can help manage the symptoms of depression, although experts are still unsure exactly how it works.

Anyone considering taking a drug or supplement that affects serotonin levels should consult their doctor first to ensure it is safe for them to use.

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