Serotonin is a neurotransmitter that regulates mood, sleep, appetite, and cognitive functions. Though primarily found in the intestines, its presence in the brain affects emotional well-being and mental health. Abnormal serotonin levels are linked to depression and anxiety.
Key Takeaways
- Serotonin is a neurotransmitter (chemical messenger) produced within the central nervous system (CNS) that contributes to feelings of happiness.
- Serotonin’s role as a neurotransmitter in the brain is important for functions, such as playing a role in mood, especially in relation to mood disorders such as depression and anxiety.
- Low serotonin levels are associated with symptoms such as depression and fatigue
- Too much serotonin, however, could result in serotonin syndrome, which could lead to symptoms of restlessness, hallucinations, and confusion.
Serotonin’s Role in the Brain
Behavior
Serotonin is projected from the brain stem and reaches most regions of the brain, giving it a wide array of effects on many aspects of behavior:
- Controls attention, perception, and memory
- Regulates anger and aggression
- Influences reward processing and motivation
- Affects motor skills and coordination
- Manages appetite and eating behaviors
- Modulates impulsivity and decision-making
Did you know? It is difficult to identify a human behavior that is not regulated by serotonin in some way.
Mood
Serotonin is one of the key neurotransmitters involved in modulating mood, since it:
- Acts as a natural mood stabilizer
- Promotes feelings of happiness and emotional stability
- Helps regulate anxiety levels
- Works with other neurotransmitters (like dopamine) to balance emotions
- Contributes to self-esteem and emotional well-being
- Influences frustration tolerance and irritability levels
Sleep
Serotonin helps regulate sleep by stimulating parts of the brain that control sleep and wakefulness:
- Controls when we fall asleep and wake up
- Regulates sleep patterns through specific brain receptors
- Serves as a precursor to melatonin production
- Different serotonin receptors determine sleep vs. wakefulness states
- Influences sleep quality and duration
Serotonin’s Role in the Body
Outside of brain functions, serotonin also plays a big role in physical health:
- Maintains digestive function
- Promotes healthy bone density
- Assists in blood clotting and wound healing
- Controls cardiovascular function
- Regulates bladder control and bowel movements
- Influences sexual function
- Helps maintain body temperature
- Affects muscle contraction and relaxation
Did you know: Most of the body's serotonin is found in the gastrointestinal tract rather than the brain.
How Does Serotonin Work?
Serotonin, also known as 5-hydroxytryptamine (5-HT), is a monoamine neurotransmitter made from the essential amino acid tryptophan.
Where It’s Made
Most of the body’s serotonin (around 90%) is produced in the gastrointestinal (GI) tract, particularly by enterochromaffin cells in the gut lining.
The remaining 10% is synthesized in the brain, specifically in a group of neurons located in the Raphe nuclei, which are clustered in the brainstem.
From the Raphe nuclei, serotonergic neurons project throughout the brain—including the limbic system, prefrontal cortex, hippocampus, and basal ganglia—allowing serotonin to influence mood, memory, learning, movement, and more.
How It Communicates
Serotonin is released from the presynaptic neuron into a tiny gap called the synaptic cleft. From there, it can do one of several things:
- Bind to serotonin receptors on the postsynaptic neuron. There are many types of receptors—such as 5-HT1A, 5-HT2A, and 5-HT3—each producing different effects depending on their location and function.
- Be taken back up by the presynaptic cell using a protein called the serotonin transporter (SERT). This process is called reuptake.
- Be broken down by an enzyme called monoamine oxidase (MAO) if not reabsorbed.
Depending on the receptor type and brain region, serotonin can be excitatory (stimulating neurons) or inhibitory (calming activity).
This is why it has such a wide range of effects—from stabilizing mood to helping regulate sleep, digestion, and blood clotting.
What Happens When Serotonin Is Low?
Low serotonin levels in the brain can affect both mental health and bodily functions, contributing to a wide range of symptoms.
This imbalance is often linked to conditions like depression, anxiety disorders, insomnia, and even irritable bowel syndrome (IBS).
Common Symptoms of Low Serotonin
When serotonin levels are low, people may experience:
- Persistent low mood or sadness
- Increased anxiety, irritability, or aggression
- Low self-esteem or negative self-perception
- Sleep problems, including insomnia or disturbed sleep
- Changes in appetite, often reduced hunger
- Poor memory or concentration
- Difficulty controlling impulses or making decisions
In more severe cases, low serotonin may also play a role in obsessive-compulsive behaviors, chronic pain, and fatigue.
Low serotonin is also associated with mood disorders such as major depressive disorder (MDD) and generalized anxiety disorder (GAD).
It may also contribute to schizophrenia, post-traumatic stress disorder (PTSD), and eating disorders.
Increasing Serotonin Levels
Increasing serotonin levels can enhance mood, alleviate depression, and regulate sleep and appetite. Proper serotonin balance is essential for emotional and mental well-being.
While medications are often prescribed to treat symptoms associated with low serotonin, there are also natural ways to boost serotonin levels:
- Exercise: Regular physical activity can increase serotonin production and release. Aerobic exercise, such as running, cycling, or swimming, has been shown to have mood-boosting effects.
- Sunlight exposure: Vitamin D, which is produced when the skin is exposed to sunlight, is important for serotonin synthesis. Spending time outdoors or using light therapy can help boost serotonin levels.
- Stress reduction: Chronic stress can deplete serotonin levels. Engaging in stress-reducing activities like meditation, yoga, or deep breathing exercises can help maintain healthy serotonin levels.
- Sleep: Adequate, quality sleep is crucial for serotonin regulation. Aim for 7-9 hours of sleep per night and maintain a consistent sleep schedule.
Medications
Selective Serotonin Re-uptake Inhibitors (SSRIs): The most prescribed antidepressants, SSRIs work by blocking the re-uptake of serotonin, making more available in the brain. Examples include Citalopram (Celexa), Fluoxetine (Prozac), and Sertraline (Zoloft).
Tricyclic antidepressants (TCAs) and Monoamine oxidase inhibitors (MAOIs): Older classes of antidepressants that also increase serotonin levels, but with more side effects compared to SSRIs.
While medications can be effective for treating serotonin imbalances, it’s important to work with a healthcare provider to find the right treatment plan.
Incorporating natural methods to boost serotonin, alongside medical treatment when necessary, can help promote overall emotional well-being.
What Happens When There’s Too Much Serotonin?
Although serotonin is beneficial in maintaining a good mood and providing people with happy feelings, too much serotonin can be detrimental.
A surplus of serotonin in the brain can be a result of the medications that are being taken to increase low serotonin levels.
Too much serotonin in the brain can result in a condition called serotonin syndrome.
This syndrome can arise after starting to take a new medication or when increasing the dosage of an existing medication.
Some of the milder symptoms associated with serotonin syndrome are as follows:
- Confusion
- Dilated pupils
- Restlessness
- Rapid heart rate
- High blood pressure
- Headaches
- Shivering and goose bumps
Mild cases of serotonin syndrome may go away within a day of stopping the medications causing the symptoms, although if not treated, it could result in worsened symptoms such as seizures, irregular heartbeat, unconsciousness, or even death in the worst cases.
Therefore, if someone is considering taking medication for curing symptoms of low serotonin or associated mental health conditions, they would be advised to start with a small dosage before potentially increasing this.
References
Berger, M., Gray, J. A., & Roth, B. L. (2009). The expanded biology of serotonin. Annual review of medicine, 60, 355-366.
Lane, R., Baldwin, D., & Preskorn, S. (1995). The SSRIs: advantages, disadvantages and differences. Journal of psychopharmacology, 9(2_suppl), 163-178.
Mayo Clinic. (2019, October 8). Tricyclic antidepressants and tetracyclic antidepressants. https://www.mayoclinic.org/diseases-conditions/depression/in-depth/antidepressants/art-20046983
Further Reading
Olivier B. Serotonin: A never-ending story. European Journal of Pharmacology. 2015;753:2-18.
