Serotonin Syndrome (Toxicity) Causes and Treatment

Symptoms of Too Much Serotonin

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 serotonin in the brain, resulting in decreased anxiety and inhibition of panic attacks. The person may feel calmer from the increased serotonin, experiencing less severe and fewer panic attacks. But, 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, that are capable of 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.


Serotonin syndrome, or serotonin toxicity, is a rare condition caused by dangerously high levels of serotonin in the brain. It can be potentially life-threatening. It is generally caused by mixing two or more medications that affect serotonin levels in the brain. SSRIs, SNRIs, tricyclic antidepressants, MAOIs, and triptans are all classes of 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
  • Loss of coordination
  • Muscle rigidity
  • Restlessness
  • Hallucinations
  • Extreme agitation
  • Fluctuations in blood pressure
  • Heart palpitations
  • Nausea, vomiting, diarrhea
  • Fever
  • Seizures
  • Coma


Since serotonin syndrome can be potentially life-threatening, emergency medical treatment is necessary. Treatment begins with the withdrawal of the causative medications. The direct effects of serotonin syndrome tend to abate in 24 to 48 hours after the drugs affecting serotonin are stopped. 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 (i.e., 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 cooling blankets and bedside fans.

Sedation: Benzodiazepines may be used to help control muscle rigidity and extreme agitation.

Hydration: Intravenous fluids may be needed to address hydration needs.

Cyproheptadine: Sometimes used to block serotonin production in the body. It has demonstrated effectiveness in reducing the severity of symptoms associated with serotonin syndrome.


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