What is serotonin and what is it’s function?

What is serotonin and what is it’s function?

Serotonin is a chemical which has a broad range of functions within the human body. Since it leads to well-being and satisfaction, it is also called the happy chemical.

Scientific name is 5-hydroxytryptamine, or 5-HT for serotonin. It is located primarily in the platelets of the brain, intestines, and blood.

Serotonin is used to transfer signals between nerve cells, it is thought to be involved in constricting smooth muscles, and it leads, among other things, to health and happiness. As the precursor to melatonin, it helps to regulate the cycles of sleep-wake and the internal clock in the body.

Appetite, impulses, and sensory, cognitive, and autonomic functions are thought to play a role. Nevertheless, it is not entirely clear how serotonin specifically influences these, or if it has an overall role in regulating the nervous system.

This appears to play a crucial role in maintaining equilibrium between the moods. Low levels of serotonin have been related to depression.

Fast facts on serotonin

  • Serotonin is an essential chemical in the human body and a neurotransmitter.
  • It is believed to help control mood and social behaviour, appetite and digestion, sleep, memory and work and sexual desire.
  • Serotonin can be related to depression. If so, it is unknown if low serotonin levels are leading to depression, or whether depression is causing serotonin levels to fall.
  • Drugs that increase serotonin levels are used to treat depression, nausea, and migraine, and can play a role in obesity and the Parkinson’s disease.
  • Other ways to improve body serotonin levels can include induction of mood, light, exercise, and diet.

What is serotonin?

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

Serotonin is produced through a biochemical conversion process, which combines tryptophan, a protein component, with a chemical reactor called tryptophan hydroxylase. They type, together, 5-hydroxytryptamine (5-HT), or serotonin.

Serotonin is most widely believed to be a neurotransmitter, though it is considered by some to be a hormone. It exists in the intestines and in the brain. It also happens in the platelets of the blood and in the central nervous system(CNS) .

Since this happens widely in the body, a number of body and psychological functions are thought to be affected.

Serotonin can not cross the blood-brain barrier, so it is important to create the serotonin that is used within the brain.


Serotonin, as a neurotransmitter, relays signals between nerve cells, or neurons, controlling their intensities.

The central nervous system (CNS) and the general functioning of the body, and especially the gastrointestinal (GI) tract, are believed to play a key role in this. Studies have established linkages between serotonin and bone metabolism, development of breast milk, liver regeneration, and cell division.

Serotonin has a strong and indirect effect on most brain cells.

Bowel function: Most serotonin in the body is located in the GI tract, where it controls bowel function and motion. It also plays a part in burning down the appetite.

Mood: Serotonin in the brain affects mood, anxiety and satisfaction levels. Illicit mood-altering drugs like ecstasy and LSD are causing large serotonin levels to increase.

Clotting: The serotonin tends to form blood clots. When a wound happens it is activated by platelets. The subsequent vasoconstriction, or blood vessel narrowing, decreases blood flow and tends to form blood clots.

Nausea: When you eat anything harmful or unpleasant, more serotonin is released by the gut to increase transit time and remove the irritant in diarrhea. It also activates the region of nausea in the brain which leads to nausea.

Bone density: Some scientists related high serotonin levels in the bones to an increase in osteoporosis, but others questioned these findings.

Sexual function: Serotonin appears to inhibit sexual behavior. Selective serotonin reuptake inhibitors (SSRIs) improve serotonin levels in people with depression, but a variety of symptoms linked to sexual dysfunction occur between 20 and 70 per cent of people who take them.

Serotonin and depression

It’s not clear exactly what induces depression, but a central hypothesis over the last 50 years is that it may include a neurotransmitter or hormone deficiency throughout the body.

Depression has been associated with low serotonin levels although it is uncertain whether this leads to or results from depression.

Food and Drug Administration (FDA) recommends SSRIs for treating depression. These are the antidepressants which are most widely prescribed. Fluoxetine (Prozac), citalopram (Celexa), and sertraline (Zoloft) are examples.

Usually, their neuronal impulse is reabsorbed into the body after a neurotransmitter has transmitted it. SSRIs prevent reabsorption of serotonin which results in higher serotonin levels in synapses.

Scientists now doubt the role of serotonin, or any other neurotransmitter, in causing depression, however.

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
Some recreational drugs increase serotonin levels.
Some recreational drugs increase serotonin levels.

These are typical symptoms of depression but little evidence exists to relate them directly to low levels of serotonin.

It may also be that this is true only for individuals already vulnerable to depressive symptoms.

When people take recreational drugs, such as MDMA and ecstasy, they release huge quantities of serotonin. This can result in loss of serotonin and a low mood, depression and other symptoms that last for several days.

Research have also shown that these medications can also harm the serotonin-containing nerves, with potentially long-lasting adverse effects.

Treatment: SSRIs

SSRIs increase serotonin levels by preventing reabsorption of the serotonin neurotransmitters. Niveaus of serotonin remain elevated in the brain. This is meant 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)

Does serotonin really relieve depression?

Since the 1980s, SSRIs have been used to treat depression by rising the serotonin levels.

Medication such as SSRIs is thought to relieve the effects of depression by increasing the body’s serotonin levels, although it’s unclear exactly how it works.

Several scientists have indicated that while SSRIs tend to function for certain individuals, increasing serotonin levels are unlikely to directly improve depressive symptoms.

One concern is that serotonin levels can be assessed in the bloodstream, but not in the brain. Scientists don’t know if bloodstream serotonin levels reflect serotonin levels in the brain, or if SSRIs can actually influence the brain.

A mouse research in 2014 indicated that serotonin does not play a part in depression. Scientists produced a few mice that did not contain serotonin in their brains. Even when put under stress, the mice showed no signs of depression.

However, in 2015 other scientists found that mice lacking serotonin were more susceptible to social stressors than mice with healthy regulation.

Although SSRIs tend to benefit certain people with depression, some scientists now claim that “simple biochemical explanations that connect low serotonin levels with depressed mood are no longer sustainable.”

One editorial published in the BMJ in 2015 refers to the use of SSRIs to treat depression as “the selling of a myth.”

SSRIs are also used to treat symptoms of anxiety, panic disorder and obsessive-compression disorder.

Adverse effects of SSRIs

SSRIs have some side effects, but these usually decrease after 2 to 4 weeks of use.

SSRIs and suicide

SSRIs don’t start working on depression for a few weeks. Symptoms of depression can intensify within the first month of treatment, before significant improvements are seen. Report any suicidal thoughts right away.

Several younger Zoloft users are also experiencing suicidal ideation.

The FDA requires all antidepressants, particularly in children, to carry a black-box warning about the danger of suicide during the initial stages of treatment.

Other uses of SSRIs

SSRIs have been used for conditions other than depression.

Treatment with serotonin may help relieve migraine
Treatment with serotonin may help relieve migraine

Antiemetics: Medications that function on serotonin receptors, such as ondansetron (Zofran), are essential for the treatment of nausea caused by chemical toxins, including chemotherapy drugs and general anesthesia. They function centrally on nausea-involved portion of the brain.

Migraine: Serotonergic vasoconstrictive antimigraine drugs, or triptans, such as almotriptan (Axert), can reduce the symptoms of migraine and are well tolerated.

Suppressants of appetite: serotonergic appetite suppressants such as fenfluramine (Pondimin) and chlorphentermine have been used to minimize appetite, although for this reason they are no longer approved.

Parkinson’s disease: The serotonergic mechanism was related to thought, emotion and motor behaviour. Therefore changes in this mechanism may have an effect on the motor and non-motor symptoms typically associated with Parkinson’s disease. Serotonergic medications were used for treating Parkinson’s disease. They are no longer licensed but work in this field continues.

Premenstrual syndrome (PMS): The cause of this disorder is unclear, but progesterone, an oversensitivity to one of the female hormones, tends to decrease serotonin levels throughout the brain. Often, serotonin antagonists are used to alleviate symptoms at the time they arise.

Other possible uses of SSRI-type drugs include the treatment of obesity and irritable bowel syndrome (IBS).

Serotonin syndrome

Serotonin syndrome, or toxicity to serotonin, can occur if a person takes two drugs that improve serotonin at the same time.

CNS and peripheral serotonin receptors get excessive stimulation. It is typically the result of a drug reaction but it may be caused by at least one medical condition.

Drug interactions: the use of prescription medications, illegal drugs or dietary supplements can lead to serotonin syndrome, for example, if a person is susceptible or if two drugs are taken concurrently that affect serotonin levels. Symptoms can occur within 6 to 8 hours of taking the medication.

Regardless of the possibility of serotinin syndrome, the FDA cautioned against taking SSRIs with triptans for testing, a drug to treat migraine.

Drugs which target serotonin levels can not be administered with MAOI’s. MAOIs are another approach to depression management which operate on multiple neurotransmitters which their receptors.

Recreational drugs: The use of recreational drugs, such as ecstasy and MDMA, leads to a high and sudden release of serotonin. This can increase the risk of serotonin syndrome when combined with prescribed serotonergic medicines.

Carcinoid tumors: These cancerous tumors, usually located in the GI tract, can induce the release of too much serotonin. There are no signs of most carcinoid tumours. They’re also found for certain conditions during studies or procedures.

Syndrome of serotonin induces excessive activity in the nerves.

Signs and symptoms include:

  • agitation and restlessness
  • confusion
  • increased heart rate and blood pressure
  • pupil dilation
  • diarrhea
  • headaches
  • shivering
  • sweating
  • loss of muscle co-ordination
  • goosebumps
  • muscle rigidity

Severe serotonin syndrome is life-threatening in 2 to 12 percent of cases.

Symptoms include a high fever, irregular heartbeat, seizures and unconsciousness.

The use of a single drug does not usually result in serotonin toxicity.


Treatment focuses on treating the symptoms and seeking to regain normal levels of serotonin.

Discontinuation of the medication can help to stop the symptoms.

Hospital care may be needed for extreme serotonin syndrome. Medicines can be given to relax or paralyze muscles, regulate heart rate and blood pressure, and often block serotonin development.

Oxygen and intravenous fluids can be administered to maintain normal bloodstream oxygen levels, and to treat fever and dehydration.

Boosting serotonin levels

As well as SSRIs and illegal drugs, there could be other ways in the body to raise serotonin levels.

Mood induction: Thought changes, either by psychotherapy or self-induction, may boost serotonin levels if the connection between serotonin synthesis and mood is a two-way relationship.

Light: Also used as a seasonal affective disorder (SAD) therapy, a few studies have indicated it can also be used to relieve depression.

Exercise: Exercise has an antidepressant effect and some work has indicated it can improve the role of brain serotonin.

Diet: Foods with higher levels of tryptophans may be related to enhanced mood and memory, likely because of elevated levels of serotonin.

Those are all areas where further research is needed, as current knowledge remains speculative.


Tryptophans are an amino acid that can be found in milk. Some research has associated a higher intake of dietary tryptophan with more positive mood scores, likely because tryptophan improves serotonin levels.

Bananas are known to contain serotonin, but is that likely to improve satisfaction in who eats them?
Bananas are known to contain serotonin, but is that likely to improve satisfaction in who eats them?

High-protein foods: Certain foods, such as beef, bacon, and cheese, are thought to contain tryptophan and to raise blood levels of tryptophan.

Bananas: These contain serotonin, and are recommended for mood raising. Even if the serotonin they produce enters the brain, they will only boost a person’s mood.

Tryptophan is a precursor, a major ingredient needed by the body to produce serotonin. Eating foods rich in this important chemicals doesn’t mean the body consumes and uses them. But providing tryptophan will boost the synthesis of serotonin when required.

However, in some studies older people who were given tryptophan supplements performed better than they had before on cognitive tests.

The idea that gut microbiota could influence the CNS and cognition through a connection known as gut-brain access is becoming increasingly of interest. In this case serotonin can be able to affect mood in the digestive system.

The following foods are said to contain tryptophans:

  • cheese
  • turkey
  • eggs
  • soya products
  • salmon
  • talbina, a dish made from barley

Nevertheless, while foods that contain tryptophan, it can make a difference in too small an quantity. Some studies have employed additional sources of tryptophan.

For example, a protein called α-lactalbumin is found in milk. It contains more tryptophan compared with other proteins. Scientists believe, however, that eating the amount that would be required to make a difference is likely not realistic.

In the 1980s, corn bred with a higher content of tryptophan was effective in preventing pellagra. Population studies indicate that there were less violent behaviors in people for whom this corn was a big part of the diet, but this may have been for other reasons. The tryptophans in the corn that increase serotonin levels in people.

Studies in which people drank beverages fortified with tryptophan and other nutrient-based therapies have provided mixed results.

There is little evidence to date that a specific diet can influence mood or depressive symptoms.

After a balanced and varied diet, however, a variety of health benefits and general well-being have been found.

The 2015-2020 Americans Dietary Guidelines encourage people to concentrate on a diverse diet and try to get as much as possible nutrients from food sources.

Tryptophan supplements are available at any medical store but should not be used without first talking to a doctor, due to the possibility of syndrome with serotonin.

Much about serotonin remains unclear. The challenges surrounding the study of brain functions means that a complete understanding of serotonin should be obtained some time ago.


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