Serotonin Uses and Side Effects

Serotonin chemicalHave you ever wondered that what control your emotions? We often think of the circumstances, belongings, or people in our lives that are responsible for our emotions, but scientifically there are certain chemicals synthesized in our bodies, which are primarily responsible for creating the sensations and emotions. Serotonin is one of the chemicals synthesized in the human body that acts as a chemical messenger and regulates various  human behavioral processes including mood perception, reward, anger, aggression, memory, and depression. It is also known as “happy chemical” because it contributes to the feelings of well being and happiness.

Happy Chemical

Chemistry of Serotonin

Scientific Name 

5-hydroxytryptamine (5-HT)

Chemical Structure


Serotonin formula

Discovery and Naming

It was first discovered by Dr. Vittorio Erspamer in Rome in 1935. Further, it was first isolated and named by Maurice M. Rapport, Arda Green and Irvine Page in 1948. It was first identified as a vasoconstrictor in the blood serum and because it is a serum agent, it was known as serotonin. Later on, the hormone was chemically identified as 5-hydroxytryptamine by Rapport and till now it is broadly known as  5-HT.

Serotonin discovery


Basically, it is a small molecule that perform two types of functions in the human body, i.e., it acts as a neurotransmitter in the central nervous system and as a hormone in the periphery. It is extensively found in the human gut, as well as in the blood stream and central nervous system. When serotonin is released by a neuron, it activates receptors located on adjacent neurons. There are many classes of 5-HT receptors and all of them are responsible for different actions.

Serotonin receptors

Biochemical Synthesis of Serotonin

The synthesis of serotonin is a biochemical process that proceeds through a multistep pathway in which L-tryptophan, a component of proteins is converted into L 5-hydroxytryptophan by an enzyme called tryptophan hydroxylase (Tph). L 5-hydroxytryptophan is then converted to serotonin by an aromatic L-amino acid decarboxylase. There are 2 types of Tph genes in our bodies, i.e., Tph1 and Tph2. Tph1 is found mostly in enterochromaffin cells of the gut (stomach) and is responsible for most of the serotonin present in the blood stream. Whereas Tph2 is found exclusively in serotonergic neurons of the brain-stream and is responsible for the production of serotonin in the brain. Brain derived serotonin (BDS) acts as a neurotransmitter, while gut derived serotonin (GDS) act as a hormone.

Biosynthesis of Serotonin

Biosynthesis of Serotonin

Tryptophan (Tph)

As discussed above, tryptophan is the starting component in the serotonin synthesis and thus, it is the important molecule for serotonin biochemical synthesis. It can not be produced by the body and so, it must be consumed through our diet. It is commonly found in foods such as nuts, fish, eggs and cheese. Tryptophan deficiency can lead to lower levels of serotonin , which in turn results in various disorders.

Tryptophan rich foods


Serotonin acts in various functions across the body, whether it is your emotions or motor skills. It impacts every part of your body.


1. Bowel Movements

Serotonin is crucial to the functions of your digestive system. Most of the body’s serotonin is produced in the gut, especially in the Gastrointestinal tract (GI tract),i.e., tract from the mouth to anus including your digestive organs. Irritable bowel syndrome (IBS) is a condition that primarily affects your large intestine, and the symptoms include abdominal cramping and pain, bloating and gas, diarrhea. People suffering from IBS who experience constipation either have lower levels of serotonin, or the muscles in their rectum are less reactive to serotonin, and they are more likely to have hard or lumpy stools. Thus, optimum levels of serotonin regulates the bowel functions and movements. It also plays a role in reducing appetite while eating.

Irritable bowel syndrome

2. Feel-Good Chemical

It plays a key role in the central nervous system (CNS). It impacts the level of mood, anxiety and happiness in the body and that’s why, it is often called as body’s natural “feel-good chemical”. Its effects in the brain could be considered as its “starring role” in the body. There are multiple serotonin receptors in the brain and each human behavior is regulated by multiple serotonin receptors. For example, anxiety like behavior is regulated by 5-HT  and 5-HT  receptors.

Feel good hormones

3. Sleep-Wake Cycles

Serotonin is the precursor of a hormone called melatonin, which is crucial to the proper functioning of your sleep cycle. As the precursor for melatonin, it helps to regulate the body’s sleep-wake cycle and the internal clock. There are specific sections in your brain that contains serotonin receptors, which controls your sleep patterns. The serotonin-melatonin relationship might also contribute to sleep disorders like insomnia.

Sleep cycles

4. Blood Clotting

The formation of blood clots in the platelets are contributed to serotonin levels in the body.  It is released by platelets when there is wound and results in vasoconstriction or narrowing of blood vessels that reduces blood flow.

5. Antidepressant

Selective Serotonin Reuptake Inhibitors (SSRI) are the most commonly prescribed medication for the treatment of depression and related mental disorders, such as Generalized Anxiety disorder (GAD), Obsessive Compulsive disorder (OCD), panic disorder, and post-traumatic disorder (PTSD). As serotonin acts as a neurotransmitter (a messenger chemical that carries nerve cells in the brain), it is usually reabsorbed by the nerve cells (known as “reuptake”) after carrying a message. SSRIs increases serotonin levels by preventing serotonin neurotransmitters from being reabsorbed. As depression and related mental conditions are caused by low levels of serotonin and a rise in serotonin levels can improve symptoms.

Serotonin as Antidepressant

Various approved SSRIs to treat depression are as follows:

Citalopram (Celexa)

Escitalopram (Lexapro)


Paroxetine( Paxil, Pexeva)

Sertraline (Zoloft)

SSRI medication

Another group of medications for depression treatment is known as serotonin-noreoinephrine reuptake inhibitors (SNRIs). Their function is similar to SSRIs but they also work on noreoinephrine (another neurotransmitter). Some SNRIs include cymbalta (duloxetine), Effexor (venlafamine), and Fetzima (levomilnacipran).

6. Parkinson’s disease

Serotonin levels in the body regulates cognition, emotion and motor behavior. The changes associated with serotonergic system may have an effect on motor and non motor features that are associated with Parkinson’s diseases.  Drugs, such as serotonergic drugs have been used to treat Parkinson’s disease. Although they are no longer licensed for treatment, the research continues in this area.

Parkinson's disease

7. Premenstrual Syndrome

Progesterone , a female hormone seems to reduce the levels of serotonin in the brain during premenstrual period. The symptoms associated with premenstrual syndrome are depressed mood, appetite changes, and food cravings and thus, serotonin inhibitors are sometimes used to relieve symptoms.



Although serotonin is considered as “happy chemical”, it has negative effects, too. Some of them are discussed below:

1. Serotonin Syndrome

It is the condition when a person consumes two serotonin-boosting drugs at the same time, or there are high levels of accumulation of chemical serotonin in the body. Some illegal drugs or dietary supplements are associated with serotonin syndrome. It results in the excessive stimulation of the CNS and peripheral serotonin receptors. Their symptoms usually occurs within several hours of taking drugs, and it includes restlessness, rapid heart rate, heavy sweating , diarrhea, headache etc.

Serotonin Syndrome

2. Sexual dysfunction

Sexual dysfunction is the common side-effect of psychotropic drugs, such as antidepressants (SSRIs). Sexual behavior in humans is influenced by dopamine and serotonin neurotransmitters. Serotonin generally inhibits the sexual activity. Microinjections of selective serotonin reuptake inhibitors (SSRI) delays the onset of sexual activity, and the major side effect of these are the impairment of ejaculatory and orgasmic ability and decreased libido, which is clinically confirmed in certain researches, and this research have important clinical implications for those taking SSRIs.


3. Carcinoid Syndrome

Carcinoid syndrome is caused by the secretion of high levels of serotonin in the blood-streams. Such syndrome is related to carcinoid tumors , which occurs mostly in the lungs or in the gastrointestinal tract including your stomach, small intestine, appendix, colon and rectum.

Carcinoid tumors

Carcinoid tumors



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