Sometimes called the “happy chemical,” serotonin is a neurotransmitter that’s been linked to mood and other functions.

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If you’re living with depression or anxiety, you may have heard that neurotransmitters can play a role in how you feel.

While many things can influence your mood, serotonin may be involved.

Everyone has different levels of this chemical. But when serotonin levels are low, you may feel sluggish, gain weight, and have trouble sleeping, among other things.

Several mental health medications work on levels of serotonin and other neurotransmitters to help improve your mood and any symptoms you have.

Serotonin — aka 5-hydroxytryptamine (5-HT) — is a chemical substance your body produces naturally. It acts both as a neurotransmitter and hormone, and it helps sends messages between your nerve cells.

Specialized nerve cells in the digestive system, brain, and spinal cord produce serotonin.

External factors may affect how much serotonin you have or produce. When you eat foods containing the amino acid tryptophan, for example, your body synthesizes it to create serotonin.

Serotonin affects several systems and functions throughout your body, from regulating your mood to helping you stay asleep.


Serotonin is believed to be a natural mood booster — that’s why it’s sometimes called a “happy chemical” or “happy hormone.”

Researchers think it plays a role in managing depression and anxiety symptoms. While the exact causes of these mental health conditions are hard to pin down, lower levels of neurotransmitters in the brain — including serotonin — have been linked.

This is known as the serotonin hypothesis.

One challenge is that experts can’t measure the amount of serotonin in the brain (only your bloodstream), so it’s difficult to know exactly how this neurotransmitter affects your mood or the right amount needed to improve it.

So far, research on the link between serotonin and mood is still mixed. Some researchers have even called the hypothesis a marketing myth.

However, the serotonin hypothesis has been the driver for two classes of antidepressant medications, both of which may help treat depression. These are selective serotonin reuptake inhibitors (SSRI) and serotonin-norepinephrine reuptake inhibitors (SNRI).


Research has shown that serotonin can:

  • suppress your appetite
  • enhance nutrient absorption
  • promote insulin secretion

All of these are factors in a functional digestive symptom. In fact, your intestines produce and store most of your body’s serotonin.

When you eat something harmful, serotonin rallies your intestines to push the offensive item through the digestive tract quickly, which makes you feel nauseous.


Serotonin, along with dopamine and melatonin, appears to play a role in three factors of rest.

Although there’s still no consensus, research in 2018 suggests that serotonin is involved in:

  • sleep preparation: helping your body and mind relax so you can fall asleep
  • sleep triggering: helping manage the circadian rhythm, including the production of melatonin
  • sleep maintenance: helping you fall asleep at regular times and stay asleep throughout the night

When serotonin levels are too low or too high, you might experience sleep disruptions.

Wound healing

Serotonin causes blood vessels to narrow, which promotes blood clotting and may help wounds heal properly.

Sexual desire

In some cases, serotonin may play a role in regulating sexual desire, along with other neurotransmitters like dopamine, norepinephrine, and oxytocin.

Research in 2016 suggests taking medications that increase levels of serotonin may be linked to lower sexual desire. This may be due, in part, to the effect serotonin has on dopamine. Increased levels of serotonin usually lead to lower dopamine activity.


According to some research, serotonin may play an important role in modulating the immune response, including inflammatory processes.

More evidence is needed to understand the exact mechanisms at play, though.


Research in 2017 suggests that serotonin may have neuroprotective effects — as in, it’s great for your brain.

Higher levels of serotonin have been associated with a slower rate of age-related cognitive decline, like dementia or Alzheimer’s disease.

The average range for serotonin blood levels is between 101–283 nanograms per milliliter (ng/mL). What happens if you fall below that range — and why would this happen?

Causes of low serotonin

There are many possible causes for someone having low serotonin levels. Some are related to genetics or lifestyle factors, including:

  • a deficiency in chemicals needed to synthesize serotonin, like L-tryptophan, omega-3 fatty acids, vitamin B6, and vitamin D
  • age-related brain changes
  • chronic stress
  • fewer serotonin receptors in your brain
  • a highly processed, low-nutrient diet
  • lack of exposure to natural light
  • exercising very infrequently
  • receptors that have a hard time receiving serotonin

Symptoms of low serotonin

Since serotonin is involved in such a wide variety of functions, there are many possible symptoms of low serotonin levels.

Mood changes

Behavioral changes

  • difficulty with memory
  • having a hard time paying attention or learning
  • hyperactivity
  • insomnia
  • a change to sexual desire

Physical changes

  • blood clotting
  • constipation
  • cravings for carbohydrates or other “comfort foods”
  • digestive issues, like irritable bowel syndrome
  • fatigue
  • premature ejaculation
  • tremors
  • weight changes

A serotonin deficiency can be addressed from multiple angles, including diet, exercise, lifestyle changes, and medication.


Since serotonin is synthesized from tryptophan in food, you may want to eat more foods with this essential amino acid.

Tryptophan-rich foods that may help you boost serotonin levels include:

  • bananas
  • eggs
  • cheese
  • nuts
  • salmon
  • tofu
  • turkey
  • pineapple
  • seeds

Lifestyle changes

Research in 2007 states that regular exercise and bright light therapy can help increase serotonin levels naturally.

For bright light, you may want to try a light therapy lamp, spending time out in the sun, or a combo of both.

To help reduce stress, you might consider adding regular relaxation techniques, exercises, and habits, like:

  • meditation and other breathing practices
  • yoga
  • self-care activities like taking a bath, spending time in nature, crafting, or whatever feels good to you

SSRI medications

If your symptoms don’t improve with diet and lifestyle changes, it’s a good idea to work with a doctor or mental health practitioner.

They can evaluate your medical history and symptoms, and if needed, give you a prescription for a selective serotonin reuptake inhibitor (SSRI).

Since serotonin can’t pass the blood-brain barrier, these medications aren’t a serotonin supplement, but they do encourage the natural production of serotonin.

Some common SSRIs include:

SNRI medications

Serotonin-norepinephrine reuptake inhibitors are a class of medications known as “dual-acting antidepressants” because they promote the production of both serotonin and norepinephrine.

Some commonly prescribed SNRIs include:

Significantly high serotonin levels are usually referred to as serotonin syndrome.

Causes of serotonin syndrome can vary, but it’s usually linked to medications meant to increase serotonin levels, like SSRIs. Research has shown it can also occur from mixing two or more drugs, like SSRIs with opioids, cold remedies, or antipsychotic meds.

Symptoms of serotonin syndrome may include:

  • agitation
  • anxiety
  • diarrhea
  • hypertension
  • muscle tissue loss
  • nausea

Significantly high serotonin levels can be life threatening. If you believe you may be having serotonin syndrome, you’ll want to seek immediate medical care, particularly if you’re having these severe symptoms:

  • confusion
  • delirium
  • hyperthermia
  • kidney disease or failure
  • respiratory difficulty or failure
  • seizures

If you have depression or anxiety, low serotonin levels may be a factor. Researchers still can’t say for sure why this is, but there does appear to be a link.

There are a handful of ways to boost serotonin levels, including making lifestyle and diet changes, relieving stress, and medications if needed.

High serotonin levels — aka serotonin syndrome — require immediate medical attention.

If you’re taking any med that might affect your serotonin production, consider discussing side effects with your doctor or a pharmacist, as well as side effects to watch out for.