What Does Serotonin Do to the Body? Role of Serotonin

Serotonin (also called 5-HT or 5-hydroxytryptamine) is a chemical that acts as a messenger between nerve cells (neurotransmitters). About 90% of serotonin is produced in the gut, and about 10% is produced in the brain.

Serotonin acts as a hormone and regulates various functions in the body by attaching to specific structures on the cells called serotonin receptors.  

The body synthesizes serotonin from tryptophan, which is an essential amino acid. Essential amino acids cannot be made by the body and must be obtained through diet or supplements.

• Mood and behavior: Serotonin plays a major role in mood regulation. It imparts a feeling of happiness and joy and helps reduce depression and anxiety. Studies report that serotonin is vital for various aspects of behavior including attention, aggression, memory, motor skills, appetite, and reward. It helps you stay calm, focused, and emotionally stable. Serotonin does not act in isolation but in coordination with other neurotransmitters such as dopamine.
• Sleep: Serotonin helps regulate your sleep-wake cycle. Serotonin receptors are present in areas of the brain that regulate body physiology and biorhythm. They help generate the sleep hormone melatonin which helps you have restful sleep.
• Digestion: Almost 90% of the serotonin in the body is produced by the gut. Serotonin helps with digestion and regulates bowel movements, which helps your body get rid of toxic substances.
• Sexual health: Serotonin along with the hormone dopamine is involved in regulating sexual functions. These hormones primarily increase sex drive.
• Wound healing: Serotonin promotes wound healing by two main mechanisms: platelet aggregation (clumping together of platelets) and vasoconstriction (narrowing of the small blood vessels at the site of the wound). It stimulates platelet aggregation, which forms the platelet plug that helps stop blood loss from the wound and promotes healing. Vasoconstriction prevents excessive blood loss at the site of the wound. 
• Bone health: High serotonin levels can cause decreased bone density. This may make your bones more brittle and increase the risk of fractures and osteoporosis.
• Nausea: Certain serotonin receptors in the brain promote nausea. This explains the use of certain drugs (such as ondansetron) that block certain serotonin receptors in the brain to reduce nausea and vomiting. The stimulation of nausea is considered a protective function to remove toxic substances from the gut.

Normal serotonin levels generally range from 50 to 200 ng/mL (0.28 to 1.14 µmol/L). 

These values may differ slightly across different labs, however, so it is important to consult your doctor about what your serotonin levels may indicate.

Low serotonin levels

Low serotonin levels can occur when your body does not produce enough serotonin or if your tissues do not respond to serotonin in the blood (resistance). This can occur due to several factors such as:

• Chronic stress
• Certain medications
• Lack of sunlight
• Dietary deficiency of the amino acid tryptophan
• Other nutritional deficiencies such as deficiency of B vitamins, vitamin D, and omega-3 fatty acids

High serotonin levels

High serotonin levels can occur in a condition called carcinoid syndrome, which refers to a group of symptoms that occur due to the secretion of various chemicals, including serotonin, by a carcinoid tumor.

An increased blood level of serotonin causes a condition called serotonin syndrome, which is generally caused by medications that cause serotonin buildup in the blood:

• Selective serotonin reuptake inhibitors
• Serotonin and norepinephrine reuptake inhibitors
• Tricyclic antidepressants
• Monoamine oxidase inhibitors
• Bupropion
• Migraine medications
• Opioid analgesics
• Lithium
• Dextromethorphan (present in over-the-counter cough and cold medications)
• Illicit drugs such as LSD, cocaine, and amphetamine
• Certain antibiotics and antiviral drugs such as linezolid and ritonavir
• Antinausea medications such as granisetron, ondansetron, and metoclopramide 
• Herbal supplements such as ginseng, nutmeg, and St John’s wort

Low serotonin levels

Low serotonin levels can cause symptoms such as:

• Low mood
• Depression
• Anxiety
• Anger or aggression 
• Reduced appetite or overeating
• Low self-esteem
• Difficulty learning and memorizing 
• Sleep disturbances
• Chronic pain
• Fatigue
• Restlessness
• Irritability
• Irrational fear or phobia 

High serotonin levels

High serotonin levels can cause symptoms such as:

• Headache
• Diarrhea
• Restlessness
• Confusion or agitation
• Muscle rigidity and twitching
• Shivering
• Sweating
• Fever
• Seizures
• Abnormal heartbeat

Your doctor may prescribe lifestyle changes and medications to increase serotonin levels. Some of the measures to treat serotonin deficiency include:

• Eating foods such as milk, cheese, eggs, pineapples, nuts, seeds, oats, tofu, and turkey
• Increasing sunlight exposure
• Regular exercise
• Dietary or supplements such as tryptophan, probiotics, nutmeg, and St John’s wort 
• Prescription medications that increase serotonin levels (such as selective serotonin reuptake inhibitors, serotonin and norepinephrine reuptake inhibitors, and tricyclic antidepressants) or block serotonin breakdown (monoamine oxidase inhibitors)