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Serotonin Syndrome

Last updated Dec. 22, 2018

Approved by: Maulik P. Purohit MD MPH

Serotonin Syndrome (SS) is a systemic condition that causes a variety of signs and symptoms due to increased activity of serotonin in the body.

What are other Names for this Condition? (Also known as/Synonyms)

  • Serotonin Toxicity Syndrome
  • SS (Serotonin Syndrome)

What is Serotonin Syndrome? (Definition/Background Information)

  • Serotonin Syndrome (SS) is a systemic condition that causes a variety of signs and symptoms due to increased activity of serotonin in the body. Serotonin is a hormone that is secreted by the body
  • The hormone plays a significant role in several body functions including sleep, digestive process, maintenance of bone health, hunger, controlling bowel movements, etc. It also helps in stabilizing the mood. Studies have shown that low levels of serotonin can lead to depression
  • Increased activity of serotonin in the body may occur due to a variety of factors including medications administered for certain health conditions, the presence of serotonin-secreting tumors, use of native medicine (herbal drugs), and use of recreational drugs such as cocaine
  • The signs and symptoms of Serotonin Syndrome may include increased sweating, flushing of the face, photophobia, diarrhea, and headaches. Severe conditions may result in increased blood pressure and also affect the heart
  • The primary method of treatment of Serotonin Syndrome involves addressing the source of serotonin imbalance in the body. If necessary, for severe cases, IV fluid administration and oxygen therapy may be recommended by the healthcare provider within a hospital setting
  • The prognosis depends on the severity of the condition. In most cases, the prognosis of Serotonin Syndrome with suitable treatment is good

Who gets Serotonin Syndrome? (Age and Sex Distribution)

  • Individuals of all ages, races, ethnic groups, and both genders are susceptible to Serotonin Syndrome
  • However, the condition develops more often in the following group of individuals:
    • Those who take medication or other herbal drugs that affect serotonin levels in the body
    • Those who are affected by carcinoid tumors
    • Or, those who are addicted to cocaine

What are the Risk Factors for Serotonin Syndrome? (Predisposing Factors)

The following conditions and factors increase an individual’s risk for Serotonin Syndrome:

  • Therapy using medications that may affect serotonin levels in the body
  • Use of combinations of drugs
  • Use of native medicines such as herbal drugs
  • Not informing your healthcare provider the full list of medicines or herbal supplements may result in SS
  • Use of illegal drugs such as cocaine
  • Any condition causing abnormal serotonin levels in the body, such as certain benign or malignant tumors

It is important to note that having a risk factor does not mean that one will get the condition. A risk factor increases one’s chances of getting a condition compared to an individual without the risk factors. Some risk factors are more important than others.

Also, not having a risk factor does not mean that an individual will not get the condition. It is always important to discuss the effect of risk factors with your healthcare provider.

What are the Causes of Serotonin Syndrome? (Etiology)

Serotonin is a hormone that is usually secreted by the stomach and intestines. It can be also secreted in the brain, helping in mood and happiness. The hormone also helps in wound-healing. Platelets in blood secrete serotonin, which assists in controlling blood loss after an injury.

Serotonin Syndrome is a disorder that is caused by a variety of factors that interfere with serotonin metabolism in the body. Such factors include:

  • Use of certain medications and drugs including:
    • Most common drugs that can result in SS are selective serotonin reuptake inhibitors (SSRIs) that are prescribed to treat depression
    • Other medications include tricyclic antidepressants (TCAs), monoamine oxidase inhibitors (MAOIs), and dextromethorphan (DXM)
    • Lithium medication therapy
    • Certain medicines to treat HIV/AIDS
    • Certain anti-nausea medications
    • Using combinations of medications without proper healthcare consultation
    • Not informing the physician about all the medications that are being taken

SS can occur either at the time of starting treatment with such medications or while increasing the dose of such medications that are already being prescribed.

  • Use of illegal drugs, such as cocaine
  • Some herbal treatment may also cause increase in serotonin levels, such as the use of St. John’s wort, nutmeg, Syrian rue, etc.
  • Increased levels can also be caused by tumor secretion; a condition termed paraneoplastic syndrome. Some such tumors secreting serotonin include carcinoid tumors of the lung, appendix, colon, small intestine, and kidney

What are the Signs and Symptoms of Serotonin Syndrome?

The signs and symptoms of Serotonin Syndrome varies from one individual to another and may include:

  • Diarrhea
  • Headache
  • Increased body temperature and increased sweating
  • Tremors
  • Flushing
  • Frequent goosebumps
  • Dilated pupils causing aversion to light

In some, the signs and symptoms of SS can be severe and may include:

  • Muscle weaknesses with twitching
  • Increased heart rate (tachycardia)
  • Increased blood pressure (hypertension)
  • Irregular heart rhythms (arrhythmias)
  • Convulsions or seizures
  • Increased levels of serotonin may result in weakening of the bones due to osteoporosis, which may result in frequent and abnormal bone fractures
  • Decreased serotonin levels lead to anxiety and sleep difficulties (insomnia)

Mild cases of Serotonin Syndrome are often underdiagnosed, due to the presence of any significant signs and symptoms.

How is Serotonin Syndrome Diagnosed?

There is no specific lab test to diagnose Serotonin Syndrome. Detecting the source of serotonin imbalance in the body is important towards establishing appropriate treatment measures. The diagnosis of SS may include the following:

  • A complete physical exam and medical history evaluation including assessment of all the current medications one is taking
  • Blood test to establish serotonin levels
  • Determining blood levels of medications being taken, analyzing current medications being taken
  • Complete blood count (CBC)
  • Radiological imaging studies to detect presence of tumors such as:
    • MRI of brain
    • CT of chest
    • USG of abdomen
  • Kidney function test to determine severity of muscle breakdown
  • Spinal tap with cerebrospinal fluid (CSF) analysis to rule out an infectious cause
  • A differential diagnosis to eliminate the following conditions may be necessary, prior to arriving at a definite diagnosis:
    • Anticholinergic toxicity
    • Heatstroke
    • Malignant hypothermia
    • Meningitis
    • Neuroleptic malignant syndrome
    • Severe alcohol withdrawal

Many clinical conditions may have similar signs and symptoms. Your healthcare provider may perform additional tests to rule out other clinical conditions to arrive at a definitive diagnosis.

What are the possible Complication of Serotonin Syndrome?

Complications that develop depend upon the severity of the signs and symptoms. In severe cases, the possible complications of Serotonin Syndrome may include:

  • Severe muscle breakdown
  • Dehydration and electrolyte imbalance in the body from severe diarrhea
  • Heart attacks
  • Convulsion can lead to body injuries (fall injuries)
  • Confusion, hallucination
  • Severe arrhythmias (irregular heart rhythms), which can result in death
  • Coma

How is Serotonin Syndrome Treated?

The treatment of Serotonin Syndrome may be undertaken as follows:

  • Managing cause of increase or decrease of serotonin in the body
  • Treating underlying conditions by effecting drug changes (i.e., changing the dose and type of drug)
  • If SS is caused by a tumor, then surgery to remove the tumor may be performed
  • Cooling the body temperature, if temperature is high
  • Administering blood pressure medications for high BP
  • Severe cases require hospitalization in an ICU setting with oxygen therapy and intravenous fluid administration

How can Serotonin Syndrome be Prevented?

In some cases, such as when caused by a tumor, Serotonin Syndrome may not be preventable. In other cases, the following preventive measures may be considered:

  • Closely monitoring the intake and dosage of medications that affect serotonin levels in the body; maintaining appropriate dosage of SSRIs
  • Regular checkups for blood level and the amount of serotonin in the body during such therapies
  • Strictly adhering to a physician’s prescription of medication; some doses which are normal to some individuals, may be high or toxic to others
  • Avoiding the use of native herbal drugs
  • Completely avoiding the usage of recreational drugs such as cocaine
  • Undertaking surgical removal (or appropriate therapy) of tumors that secrete serotonin

In case of low levels of serotonin, the following natural methods may be considered, to increase levels of the hormone in the body:

  • Regular exercise
  • Healthy diet
  • Regular exposure to sunlight and/or bright lights
  • Meditation

What is the Prognosis of Serotonin Syndrome? (Outcomes/Resolutions)

The prognosis of Serotonin Syndrome depends on the severity of signs and symptoms and the presence of any complications.

  • In a majority of cases, the prognosis is good with adequate treatment
  • The development of severe heart abnormalities may adversely affect the prognosis
  • Muscle pain and weakness may be present for several months before getting better

Additional and Relevant Useful Information for Serotonin Syndrome:

The following link will help you with more information on serotonin blood test:


What are some Useful Resources for Additional Information?

References and Information Sources used for the Article:

Helpful Peer-Reviewed Medical Articles:

Reviewed and Approved by a member of the DoveMed Editorial Board
First uploaded: April 30, 2017
Last updated: Dec. 22, 2018