Serotonin Syndrome: What Happens If You Have Too Much Serotonin?

Close-up of Prozac, Paxil, and Zoloft tablets.

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Too much serotonin can be dangerous and even life-threatening. Certain medications can lead to high levels of serotonin in the body and can trigger a condition called serotonin syndrome.

Serotonin Syndrome: Signs of Too Much Serotonin

Serotonin is a neurotransmitter that helps stabilize mood, is often associated with feelings of happiness, and plays a role in sleep quality, memory, and sexual desire. However, too much serotonin can lead to harmful effects. These effects are known as serotonin syndrome.

Signs of Too Much Serotonin

If you've had too much of a serotonin-increasing drug or take more than your prescribed dosage, you may experience symptoms of serotonin toxicity.

Signs include:

  • Confusion
  • Increased reflexes
  • Restlessness
  • Hallucinations
  • Extreme agitation
  • Fluctuations in blood pressure
  • Increased heart rate
  • Nausea, vomiting, and diarrhea
  • Fever
  • Seizures
  • Coma

When Do Signs of Serotonin Syndrome Begin?

Symptoms of serotonin syndrome can begin within minutes, a few hours, or up to 24 hours after taking or increasing the dose of a medication.

Most individuals experiencing symptoms of serotonin syndrome will seek emergency treatment within six hours.

If you or a loved one begin experiencing symptoms of serotonin toxicity, call 911 and head to your nearest emergency room immediately.

What Causes Serotonin Syndrome?

Serotonin syndrome, or serotonin toxicity, is a rare and potentially life-threatening condition caused by dangerously high serotonin levels in the brain. It's generally caused by taking two or more medications that raise serotonin levels (aka serotonergic drugs) in the central nervous system.

Substances that may contribute to excess serotonin levels include:

  • Some types of antidepressants
  • Triptan migraine medications
  • Illicit drugs such as cocaine, lysergic acid diethylamide (LSD), amphetamines, and ecstasy
  • Herbal supplements such as St. John's wort, nutmeg, and ginseng
  • Certain cold medications
  • Some anti-nausea medications

SSRIs, SNRIs, tricyclic antidepressants, and monoamine oxidase inhibitors (MAOIs) are all classes of antidepressant medications that have been known to lead to serotonin syndrome.

These antidepressants are often prescribed to treat depression and anxiety disorders, including panic disorder.

Potential Effects of Serotonin Syndrome

If you've had too much serotonin, some effects (although rare) may include:

  • Organ damage (permanent)
  • Muscle spasms (this can lead to the breakdown of your muscles)
  • Kidney damage

Can Too Much Serotonin Cause Anxiety?

It is possible that drugs containing serotonin can lead to anxiety. For instance, anxiety is a potential side effect of Prozac (fluoxetine).

Serotonin Syndrome Treatment

Since serotonin syndrome can be potentially life-threatening, emergency medical treatment is necessary. Treatment often begins with the withdrawal of the medications that lead to your high serotonin levels.

However, some complications, such as delirium, unstable heart rate, high blood pressure, and high temperature may persist longer.

Supportive measures and interventions in a hospital setting may be necessary and include:

  • Heart rate and blood pressure control: Medications may be needed to decrease heart rate and blood pressure. On the other hand, medications may be given to raise blood pressure if it is too low.
  • Temperature control: Fever may be treated with cooling blankets.
  • Sedation: Benzodiazepines may be used to help control muscle rigidity and extreme agitation.
  • Hydration: Intravenous fluids may be needed to address dehydration caused by high body temperature and sweating.
  • Cyproheptadine: This antihistamine is sometimes used to block serotonin production in the body. It's been shown to reduce the severity of symptoms associated with serotonin syndrome.

Serotonin Syndrome Prevention

To prevent serotonin syndrome, be sure to tell your doctor about all of the medications you are taking prescription drugs, over-the-counter medications, and supplements.

If you're taking a medication that impacts serotonin levels, talk to your doctor about your risk of developing serotonin syndrome.

4 Sources
Verywell Mind uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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By Sheryl Ankrom, MS, LCPC
Sheryl Ankrom is a clinical professional counselor and nationally certified clinical mental health counselor specializing in anxiety disorders.