Serotonin (5-hydroxytryptamine) is a tissue hormone and a neurotransmitter (transmitter substance for nerve cells).


Serotonin is a hormone and neurotransmitter, i.e. a messenger substance of the nervous system. Its biochemical name is 5-hydroxy-tryptophan, which means that serotonin is a derivative of the amino acid tryptophan. The effect of a hormone and neurotransmitter always depends on its receptors on the target cells. Since serotonin can bind to several receptors, it has a very wide spectrum of activity, and it is mainly found in the brain stem.


Formation of serotonin:

The hormone serotonin is synthesized from the amino acid tryptophan via the intermediate product 5-hydroxy-tryptophan, which happens either in nerve cells of the brain or in specialized cells such as the enterochromaffin cells of the intestine. The serotonin in the intestinal cells is broken down by monoamine oxidase (MAO) and other enzymes which form the end product 5-hydroxyindole acetic acid.
This breakdown product is ultimately excreted with the urine. In its function as a neurotransmitter, serotonin is taken up again in the nerve cell that releases it and is thus reused.
Serotonin is also the starting point for the synthesis of the hormone melatonin, which is found in the pineal gland (Epiphysis) will be produced.
The receptors that match serotonin are cell surface receptors or ion channels.


Serotonin acts as an intermediary between nerve cells and in this way transmits information. It is best known for its mood-enhancing effect, which is why it is often referred to as the "happiness hormone". In fact, it plays a huge role in our limbic system. This is the system in which our emotions are processed.

Read more on this topic: The role of serotonin / neurotransmitters in depression

If a lot of serotonin is produced and released, we feel happy. But it can do even more. It has an inhibitory effect on the nerves that transmit pain and controls, among other things, the human sleep-wake rhythm. In addition, serotonin is a hormone, i.e. a messenger substance that takes on tasks outside of the nervous system. In its function as a hormone, it is involved in the regulation of blood flow to organs and promotes the movements of the intestine.



The serotonin release is stimulated in a tissue-specific manner, for example when the Platelets (Platelets) distributed. The effect is terminated when the hormone is broken down or reabsorbed in the nerve cells.


Serotonin is characterized by many effects. These partly contradicting (antagonistic) Mode of action of the hormone through the many different serotonin receptors.
Serotonin affects that Cardiovascular system, the gastrointestinal tract, blood clotting, that central nervous system, the Intraocular pressure as well as cell growth.
Depending on the organ, this makes it possible hormone either a narrowing of the blood vessels (Constriction) or an extension (Dilation). After the action of serotonin, blood vessels expand in the muscles so that blood flow is increased. In lung or Kidneys on the other hand, the effect of hormones results in a constriction of the blood vessels. Overall, the influence of serotonin on systemic blood pressure is complex. Effects are achieved both directly on the blood vessels and via the central nervous system, which interact with the level of blood pressure.

In the gastrointestinal tract, serotonin acts directly as a hormone on the one hand, and as a nerve transmitter on the other (Transmitter) of the enteric nervous system (Intestinal nervous system). Promotes its function as a neurotransmitter Serotonin the motility of the intestines and the transport of the food pulp (peristalsis), which occurs through alternating tension and relaxation of the intestine. Also the stimulus too nausea and Vomit and the information about pain in the intestinal area is transmitted serotonically controlled.

The second mode of action as a hormone begins with the release of the Serotonins from the enterochromaffin intestinal cells. After eating, the hormone is released due to the increased pressure inside the intestine (Intestinal lumen) released through the food pulp, so that digestion and the passage of food are made possible by the associated increase in peristalsis.
Regarding blood clotting, serotonin stimulates by increased clumping of blood platelets (Platelet aggregation) the coagulation. If a clot forms (thrombus) the hormone is extracted from the platelets that bind to it (Platelets) released and causes a constriction of the blood vessels (Vasoconstriction) as well as promoting coagulation. Serotonin also acts as an enhancer for other substances that promote blood clotting.

The so-called serotonergic system exists in the central nervous system. The origin of this system can be found in special nerve nuclei, the raphe nuclei of the Brain.
These nerve nuclei are distributed throughout the brain stem. Serotonin is involved in the regulation of sleep, mood, temperature, pain processing, appetite and sexual behavior.

In particular, the hormone promotes wakefulness. It is released more when you are awake, but hardly when you are asleep. Involved in the regulation of the sleep-wake rhythm is that in the pineal gland (Epiphysis) produced the hormone melatonin.
Further decreased Serotonin the appetite, which is controlled by the tryptophan concentration in the blood. When it rises, it increases insulin released so that the tryptophan is absorbed into the cerebral circulation (via the Blood-brain barrier) is stimulated. The oversupply of tryptophan increases the production of serotonin, which has an appetite suppressant effect.

Regarding mood, serotonin can euphoric Hallucinations evoke and inhibit impulsive or aggressive behavior. The feeling of anxiety and depressive moods will be through Serotonin reduced.
The processing of pain and the level of body temperature are also regulated by serotonin; sexual behavior and functions are inhibited.
Serotonin also promotes wound healing by stimulating the growth of certain cells. This effect as a growth hormone can also be found in heart cells (Myocytes), which is also used by serotonin to increase (proliferation) are stimulated.
It also has serotonin in humans eye certain functions. It is responsible for the intraocular pressure, which is presumably regulated by the pupil size and the amount of aqueous humor. When the formation of aqueous humor increases, the pressure inside the eye increases, as does the enlargement of the pupil, since this obstructs the drainage path of the aqueous humor.
An increased serotonin level after consuming chocolate is discussed. This could be explained by the tryptophan contained in chocolate, which is converted into serotonin by the body, so that the serotonin concentration increases.
This is used to explain the mood-enhancing effects of chocolate. Another opinion, however, says that it is not the tryptophan in chocolate, but the high amount of it Carbohydrates is responsible for raising the mood.

Diseases caused by malfunction


Serotonin is, among other things, in connection with the emergence of depressions and migraine brought.
Depression is a mood disorder and is a state of joylessness and dejection. This includes an inhibition of drive, thought disorders and insomnia. In depression, a lack of serotonin is discussed as one of the causes of the development of the disease, although this is not fully understood.
It was observed in those affected that the serotonin uptake in the brain and in the blood platelets is reduced, which was attributed to a genetically modified serotonin transporter.
Migraine is a disease with recurring unilateral a headache pulsating character. In addition, other complaints such as nausea, Vomit, Sensitivity to light and noise (photophobia, phonophobia) accompany the pain. Before this, a so-called aura can occur, which is characterized by visual or hearing impairments, sensory or motor deficits. Before and after a migraine attack, varying levels of serotonin levels were observed in sick people, with a low level probably promoting the spread of the headache.

Serotonin Syndrome

Serotonin can be given in small doses as a drug, for example when someone is suffering from depression. However, if the permitted daily dose that may be taken is exceeded or if serotonin can no longer be correctly or completely broken down, it will accumulate in the body and trigger the serotonin syndrome.

Syndrome means that there are many different symptoms occurring at the same time. The serotonin syndrome initially manifests itself in symptoms that are similar to those of a flu-like infection. People get a fever, sweat and shiver, their pulse rises and they feel sick. If you cannot intervene quickly enough, massive effects such as seizures and hallucinations occur.

The only therapy is to immediately discontinue the administered drug and administer serotonin antagonists. However, since serotonin cannot be detected directly, for example by means of a blood test, it is not always easy to recognize the serotonin syndrome as such immediately.

You can find much more information at: Serotonin Syndrome

What is the antagonist to serotonin?

One possibility to treat the serotonin syndrome is the administration of serotonin antagonists. These are substances that do exactly that opposite effect to have serotonin. Most antagonists work by blocking the receptors that serotonin binds to. As a result, it can no longer develop its effect on the target cell on which the receptor is located. In the human body there are no substances that directly antagonistic to serotonin are, however, there are synthetically produced Antagonists that can be taken as drugs.

Deficiency of serotonin

A Deficiency of serotonin can focus on various ways to make noticable. In the brain, a lack of serotonin leads to too sleep disorders, depressions and probably also for the development of Anxiety disorders. Since serotonin also plays a role in the intestine, it is assumed that a drop in the serotonin concentration can lead to digestive problems and irritable bowel symptoms.

Serotonin levels

The serotonin level indicates how much serotonin is in the body. Depending on the illness, it can be greatly reduced or increased, with medication and drugs also influencing the level. It is now known that serotonin levels in diseases such as depressions and Parkinson's disease, as well as in various anxiety states is massively reduced.

Serotonin levels rise in the context of serotonin syndrome or drug abuse. In the case of drugs, this fact manifests itself in exaggerated motivation, increased mood and increased willingness to take risks. The body and the human psyche can also get used to a new, changed serotonin level over time.

It is also very difficult for patients who have been taking pain-relieving drugs such as opioids for a long time to stop, because they are so concerned about the better mood and the complete painlessness used have that they go without the medication relatively Feeling "unhappy".

How can you measure serotonin levels?

Serotonin levels cannot be measured directly. Evidence in the blood is very inaccurate and hardly allows any conclusions to be drawn about diseases. So far, no method has been developed with the help of which one could determine the absolute serotonin content of the body. One of the reasons for this is that serotonin is practical hardly free in the blood is to be found.

The largest proportion is stored in the thrombocytes (blood platelets). The examination of cerebrospinal fluid cannot provide precise values ​​either, since only about 1% of the total serotonin in the body is stored in the nerve cells of the brain. So you know the distribution, but not the one absolute quantitiesin which serotonin is present.

How can you increase serotonin levels?

There are many ways to increase serotonin levels. One possibility is to take drugs that bind to the various serotonin receptors, thereby mimicking the effects of serotonin.

Such substances are called serotonin agonists or 5-HT agonsites. By binding the agonist to the cell, the cell believes that serotonin is at the receptor and the same subsequent mechanisms are triggered that serotonin itself would have set in motion.

On the other hand, there are drugs that inhibit the breakdown of serotonin, which causes the concentration to rise steadily. To understand the third pharmacological way of increasing serotonin levels, one has to look at the exact sequence of serotonin release. Serotonin is released as a messenger substance by a nerve cell in order to then bind to the receptors of an adjacent cell.

This bond is only brief and as soon as the serotonin is free again between the two cells, it is completely absorbed again by the first cell so that it can then be reused. This reuptake can be prevented by so-called reuptake inhibitors, which increases the concentration of serotonin in the space between the two cells.

Read more about this under Cipralex®

Foods containing serotonin

As mentioned earlier, serotonin is a derivative of the amino acid tryptophan, which means that the body does Tryptophan needed to be able to produce serotonin from it. Serotonin is contained in some foods, but cannot as such Blood-brain barrier overcome and therefore does not significantly contribute to the rise in serotonin levels. It is completely different when you eat foods that contain the precursor tryptophan. Foods containing tryptophan are for example nuts, kernels, grains, various types of cheese such as Edam and Parmesan and chocolate. They are able to raise the serotonin level to a certain extent.

Serotonin vs. Dopamine

Dopamine is another neurotransmitter of the brain. It occurs in the basal ganglia as well as the limbic system where it occurs Thinking and perception processes is involved and plays an important role in controlling movements. On the one hand, serotonin and dopamine, as neurotransmitters, are active in different areas of the brain with very different effects. This can be seen particularly in the diseases that occur when there is a deficiency in one of the two substances.

in case of an Serotonin deficiency in the brain, as already mentioned above, it can become too depressive symptoms, up to manifest depression. However, if there is a dopamine deficiency, it comes to the occurrence of Parkinson's, a disease that is mainly characterized by a lack of coordination, tremors and movement disorders.

On the other hand, dopamine and serotonin work in general stimulating and promoting on the structures of the systems in which they are involved. Sometimes they even work in parallel, so to speak. Again, this fact becomes clear with the help of diseases. Mild to moderate depression is another symptom of Parkinson's disease.


Symptoms of depression include loss of interest, listlessness, and dejection. In addition, there may be other symptoms such as tiredness, disturbed sleep, loss of appetite and difficulty concentrating.

Depending on the extent of the symptoms, a distinction can be made between mild and moderate to severe depression. The cause is still not completely clarified, however, it is certain that depression comes with one decreased serotonin and norepinephrine levels go hand in hand, which is why the most common drugs target one Increase in concentration target of these two neurotransmitters.

Depression can be called independent illness occur, but also be the symptom of another disease, such as Parkinson's disease or the Chorea huntington.