What is serotonin and what does it do?

Serotonin is a chemical that has a wide variety of functions in the human body. It is sometimes called the happy chemical, because it contributes to wellbeing and happiness.

The scientific name for serotonin is 5-hydroxytryptamine, or 5-HT. It is mainly found in the brain, bowels, and blood platelets.

Serotonin is used to transmit messages between nerve cells, it is thought to be active in constricting smooth muscles, and it contributes to wellbeing and happiness, among other things. As the precursor for melatonin, it helps regulate the body’s sleep-wake cycles and the internal clock.

It is thought to play a role in appetite, the emotions, and motor, cognitive, and autonomic functions. However, it is not known exactly if serotonin affects these directly, or if it has an overall role in co-ordinating the nervous system.

It appears to play a key role in maintaining mood balance. Low serotonin levels have been linked to depression.



Fast facts on serotonin

  • Serotonin is an important chemical and neurotransmitter in the human body.
  • It is believed to help regulate mood and social behavior, appetite and digestion, sleep, memory, and sexual desire and function.
  • There may be a link between serotonin and depression. If so, it is unclear whether low serotonin levels contribute to depression, or if depression causes a fall in serotonin levels.
  • Drugs that alter serotonin levels are used to treat depression, nausea, and migraine, and they may have a role in obesity and Parkinson’s disease.
  • Other ways to increase body serotonin levels may include mood induction, light, exercise, and diet.

What is serotonin?

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Can serotonin boost happiness, or is it more complex than that?

Serotonin is created by a biochemical conversion process that combines tryptophan, a component of proteins, with tryptophan hydroxylase, a chemical reactor. Together, they form 5-hydroxytryptamine (5-HT), or serotonin.

Serotonin is most commonly believed to be a neurotransmitter, although some consider it to be a hormone. It is produced in the intestines and the brain. It is also present in the blood platelets and the central nervous system (CNS).

As it occurs widely throughout the body, it is believed to influence a variety of body and psychological functions.

Serotonin cannot cross the blood-brain barrier, so any serotonin that is used inside the brain must be produced inside the brain.


As a neurotransmitter, serotonin relays signals between nerve cells, or neurons, regulating their intensity.

It is believed to play a key role in the central nervous system (CNS) and in the general functioning of the body, and especially the gastrointestinal (GI) tract. Studies have found links between serotonin and bone metabolism, breast milk production, liver regeneration, and cell division.

Serotonin influences most brain cells both directly and indirectly.

Bowel function: Most of the body’s serotonin is found in the GI tract, where it regulates bowel function and movements. It also plays a part in reducing the appetite while eating.

Mood: In the brain, serotonin impacts levels of mood, anxiety, and happiness. Illicit mood-altering drugs such as Ecstasy and LSD cause a significant rise in serotonin levels.

Clotting: Serotonin contributes to the formation of blood clots. It is released by platelets when there is a wound. The resulting vasoconstriction, or narrowing of the blood vessels, reduces blood flow and helps blood clots to form.

Nausea: If you eat something that is toxic or irritating, the gut produces more serotonin to increase transit time and expel the irritant in diarrhea. This also stimulates the nausea area in the brain, resulting in nausea.

Bone density: Some scientists have linked high levels of serotonin in the bones to an increase in osteoporosis, but others have challenged these results.

Sexual function: Serotonin appears to inhibit sexual activity. Selective serotonin reuptake inhibitors (SSRIs) boost serotonin levels in people with depression, but between 20 and 70 percent of people who take them experience a range of symptoms related to sexual dysfunction.

Serotonin and depression

It is not clear precisely what causes depression, but a key theory in the last 50 years is that it may involve an imbalance of neurotransmitters or hormones in the body.

Depression has been linked to low levels of serotonin, but whether this contributes to depression or results from it remains unclear.

SSRIs are approved by the Food and Drug Administration (FDA) to treat depression. They are the most commonly prescribed antidepressants. Examples include fluoxetine (Prozac), citalopram (Celexa) and sertraline (Zoloft).

Normally, once a neurotransmitter has transmitted its neural impulse is reabsorbed into the body. SSRIs prevent the serotonin from being reabsorbed, leading to higher levels of serotonin in the synapses.

However, scientists are now questioning the role of serotonin or any single neurotransmitter in triggering depression.

Serotonin deficiency symptoms

Low levels of serotonin have been linked with:

  • poor memory
  • low mood

They may also lead to the following symptoms:

  • craving for sweet or starchy foods
  • difficulty sleeping
  • low self-esteem
  • anxiety
  • aggression

recreational drugs increase serotonin levels.

Some recreational drugs increase serotonin levels.

These are common symptoms of depression, but there appears to be little evidence linking them directly to low serotonin levels.

It may also be that this is only true for people who are already susceptible to the symptoms of depression.

When people use recreational drugs, such as MDMA and ecstasy, large amounts of serotonin are released. This can lead to serotonin depletion and a low mood, confusion, and other symptoms that last several days.

Studies have also shown that these drugs may also damage the nerves that contain serotonin, with possible long-lasting adverse effects.

Treatment: SSRIs

SSRIs increase serotonin levels by preventing serotonin neurotransmitters from being reabsorbed. Serotonin levels remain high in the brain. This is believed to elevate mood.

SSRIs that the FDA has approved to treat depression are:

  • Citalopram (Celexa)
  • Escitalopram (Lexapro)
  • Fluoxetine (Prozac)
  • Paroxetine (Paxil, Pexeva)
  • Sertraline (Zoloft)
  • Vilazodone (Viibryd)
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