Serotonin Syndrome (Toxicity)

Prozac, Paxil and Zoloft anti-depressant tablets, close-up

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The antidepressants called selective serotonin reuptake inhibitors (SSRIs) are considered to be first-line agents in the treatment of panic disorder and other anxiety disorders. SSRIs increase the level of available serotonin in the brain, resulting in decreased anxiety and inhibition of panic attacks. However, if serotonin levels increase too much, a serious medical condition called serotonin syndrome may result.

The human brain is believed to function in a complex chemical environment through various types of neurons and neurotransmitters. Neurons are brain cells, numbering in the billions, capable of near-instant communication with each other through chemical messengers called neurotransmitters. Serotonin is one of these chemical messengers. It plays a role in modulating anxiety, mood, sleep, appetite, and sexuality. Serotonin is also produced in the digestive tract, playing a role in digestion and other bodily processes.

What Is Serotonin Syndrome?

Serotonin syndrome, or serotonin toxicity, is a rare and potentially life-threatening condition caused by dangerously high levels of serotonin in the brain. It's generally caused by mixing two or more medications that affect serotonin levels in the central nervous system.

SSRIs, SNRIs, tricyclic antidepressants, and MAOIs are all classes of antidepressant medications that have been implicated in the development of serotonin syndrome. These antidepressants are often prescribed to treat depression and anxiety disorders, including panic disorder.

Signs and Symptoms

Signs and symptoms of serotonin syndrome include:

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


Since serotonin syndrome can be potentially life-threatening, emergency medical treatment is necessary. It begins with the withdrawal of the medications causing the dangerously high levels of serotonin.

However, some of the complications, such as delirium, and instability of heart rate, blood pressure, temperature, and other functions of the autonomic nervous system, may persist longer. Supportive measures and interventions in a hospital setting may be necessary and include:

  • Heart rate and blood pressure control: Medications to decrease heart rate and blood pressure (esmolol or nitroprusside) may be needed. Medications may also be given if blood pressure is too low.
  • Temperature control: It may be necessary to treat fever symptoms with methods such as cooling blankets.
  • Sedation: Anti-anxiety drugs like benzodiazepines may be used to help control muscle rigidity and extreme agitation.
  • Hydration: Intravenous fluids may be needed to address hydration needs 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.


  • Tell your doctor about all of the medications you are currently taking. This includes prescription drugs, over-the-counter medications, and supplements.
  • If you're taking a medication that affects serotonin levels, talk to your doctor about your risks for developing serotonin syndrome.
  • Seek immediate medical care if you're taking a medication that affects serotonin levels and you develop any of the symptoms of serotonin syndrome.
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