HormonesMood and Mental Health

Serotonin – The happiness hormone

Written by

Anna Roell
18 July, 2023

Medically checked article All HOMED-IQ content is reviewed by medical specialists

Neurotransmitters are chemical messengers in the brain that play a vital role in communication between neurons, the specialized cells of the nervous system. They transmit signals across synapses, which are the tiny gaps between neurons. One well-known neurotransmitter is serotonin, often referred to as the “feel-good” neurotransmitter. Responsible for a variety of functions ranging from mood regulation to digestion, serotonin is a key player in our well-being. Serotonin levels that are too low or too high can lead to physical and mental health problems. Read on to learn more about what serotonin is and the effects it has on our bodies and moods.

What is serotonin?

Serotonin is a neurotransmitter that plays a crucial role in various bodily functions. It is produced from the essential amino acid tryptophan, which we obtain from our diet. Serotonin plays a crucial role in many aspects of our lives, from our mood to our physical health. Adequate serotonin levels can help counteract depression and anxiety, and generally promote our mental health. But serotonin isn’t just limited to our brains. In fact, about 90% of our body’s serotonin is found in the gut, where it plays a key role in regulating bowel movements (Cleveland Clinic, 2022).

The multiple functions of serotonin

Serotonin acts as a regulator of numerous bodily functions. Below are some of the most important functions:

  1. Mood regulation: serotonin affects our mood and overall sense of well-being. In the brain, serotonin influences mood, anxiety, and happiness. Balanced serotonin levels are associated with feelings of focus, happiness, and contentment.
  2. Sleep-wake cycle: Serotonin plays a critical role in regulating the sleep-wake cycle and sleep quality. Serotonin is a precursor to the sleep hormone melatonin.
  3. Appetite control: Serotonin also helps control appetite and satiety. It affects how full we feel after eating and can control cravings for certain foods.
  4. Digestion: Over 90% of our serotonin is produced in the gut, where it plays an essential role in regulating digestive functions.

Source: Berger et al., 2009

Changes in serotonin levels

Because serotonin plays a central role in a variety of bodily functions, such as regulating our mood and aiding our digestion, the levels of serotonin in our bodies can have a significant impact on our health and well-being.

Causes of low serotonin levels

Low serotonin usually has more than one cause, and can occur if the body does not produce enough serotonin or is unable to utilize serotonin properly, for example due to too few serotonin receptors (Cleveland Clinic, 2022). A lack of sunlight, unhealthy diet, stress, and certain medications are associated with lowered serotonin levels (Young, 2007).

Consequences of low serotonin levels

A lack of serotonin in the brain can lead to a variety of symptoms and health problems. Here are some of the most common symptoms that can occur when serotonin levels in your body are lower than normal:

  1. Depression and anxiety: Low serotonin levels have been associated with depression and anxiety disorders, as well as related symptoms such as irritability, panic attacks, and mood swings (Bocchio et al., 2016).
  2. Sleep disorders: Because serotonin plays an important role in regulating the sleep-wake cycle, low serotonin levels are associated with sleep disorders such as insomnia (difficulty falling and staying asleep) (Ursin, 2002).
  3. Memory problems: Research has shown that serotonin plays a role in cognitive function, including memory and learning. Low serotonin levels could therefore cause problems with memory and focus (Healthdirect, 2021).
  4. Digestive problems: Since serotonin is also produced in the intestines and plays a role in regulating digestion, low serotonin levels can lead to digestive problems such as constipation or diarrhea (Cleveland Clinic, 2022).

It is important to note that the health problems associated with low serotonin levels are non-specific and may be caused by other health problems. If you are experiencing any of the above symptoms, consult a physician to determine the underlying cause.

Causes of high serotonin levels

High serotonin levels can occur due to a rare, serious drug reaction known as serotonin syndrome. This condition is caused by taking medications that increase levels of serotonin in the body, such as antidepressants. Serotonin syndrome often occurs when taking a new medication or increased dosage of an existing medication. Serotonin syndrome is a potentially life-threatening condition that requires immediate medical attention and stopping the medication immediately. Symptoms of serotonin syndrome can range from mild (such as tremors and diarrhea) to severe (such as high fever, fainting, and loss of consciousness) (Mayo Clinic, 2022).

Maintaining balanced serotonin levels

There are several ways to maintain healthy serotonin levels:

  • Follow a balanced diet: a diet rich in tryptophan-containing foods, such as nuts, seeds, tofu, cheese, red meat, chicken, turkey, fish, oats, beans, lentils, and eggs, can help support healthy serotonin levels.
  • Regular exercise: Sports and other physical activities can stimulate the production of serotonin.
  • Bright light exposure: Daylight, especially morning light, can boost serotonin production.

Source: Cleveland Clinic, 2022

It is important to seek professional medical help if you feel that your serotonin levels are out of balance, especially if you are experiencing mental health symptoms including depression, anxiety, panic, or sleep disorders.

Drug treatment for serotonin imbalances

In some cases, when the natural balance of serotonin is disrupted, medication may be necessary to relieve symptoms. Serotonin-increasing medications are only ever prescribed after an examination by a physician, who will determine whether you can benefit from these medications. A well-known approach to treating serotonin imbalances is the use of antidepressants, such as selective serotonin reuptake inhibitors (SSRIs) or serotonin and norepinephrine reuptake inhibitors (SNRIs). These medications increase the amount of serotonin in your brain. SSRIs are often used to treat depression and anxiety disorders. Treating serotonin imbalances can be complex and requires an individualized approach (MedicalNewsToday, 2020).

What is the difference between serotonin and dopamine?

Serotonin and dopamine are both neurotransmitters that play a role in regulating mood and behavior. Although they have similar functions, they differ in their exact actions in the body. While serotonin is largely responsible for feelings of satisfaction and well-being, dopamine is associated with reward, motivation, and pleasure (Cleveland Clinic, 2022). The balance of these two neurotransmitters is important to our emotional and physical health. Imbalances can lead to various health problems ranging from mild unhappiness to severe mental health problems.

In summary, serotonin plays a central role in our bodies and influences the regulation of our mood, sleep, appetite and many other bodily functions. Adequate serotonin levels are therefore of great importance for our general well-being and health.


Berger, M., Gray, J.A., & Roth, B.L. (2009). The Expanded Biology of Serotonin. Annual review of medicine, 60, 355-366. https://doi.org/10.1146/annurev.med.60.042307.110802

Bocchio, M., Fucsina, G., Oikonomidis, L., McHugh, S.B., Bannerman, D.M., Sharp, T., & Capogna, M. (2016). Serotonin, Amygdala and Fear: Assembling the Puzzle. Frontiers in neural circuits, 10, 24. https://doi.org/10.3389/fncir.2016.00024

Moawad, H. (n.d.). Serotonin deficiency: Symptoms, treatments, causes, and more. Medical News Today. Retrieved June 12, 2023, from https://www.medicalnewstoday.com/articles/serotonin-deficiency#symptoms

Moawad, H. (n.d.). Serotonin deficiency: Symptoms, treatments, causes, and more. Medical News Today. Retrieved June 12, 2023, from https://www.medicalnewstoday.com/articles/serotonin-deficiency#summary

Serotonin | healthdirect. (n.d.). Healthdirect. Retrieved June 12, 2023, from https://www.healthdirect.gov.au/serotonin

Serotonin syndrome – Symptoms and causes. (2022, January 22). Mayo Clinic. Retrieved June 12, 2023, from https://www.mayoclinic.org/diseases-conditions/serotonin-syndrome/symptoms-causes/syc-20354758Serotonin: What Is It, Function & Levels. (2022, March 18). Cleveland Clinic. Retrieved June 11, 2023, from https://my.clevelandclinic.org/health/articles/22572-serotonin

About the author

Anna Roell

Anna is a trained nurse and health economist specializing in epidemiology, combining her medical and scientific interests. Her goal is to improve others' understanding of medical information and to communicate it in an understandable way. Anna is originally from Germany and now lives in Amsterdam. What she appreciates most about Amsterdam is the open-minded, active attitude of the people, the markets, and the beautiful nature in the areas surrounding Amsterdam.