Serotonin syndrome
Hyperserotonemia; Serotonergic syndrome; Serotonin toxicity; SSRI - serotonin syndrome; MAO - serotonin syndromeSerotonin syndrome (SS) is a potentially life-threatening drug reaction. It causes the body to have too much serotonin, a chemical produced by some nerve cells.
Causes
SS most often occurs when two or more medicines or drugs that affect the body's level of serotonin are taken together at the same time. The medicines cause too much serotonin to be released or to remain in the brain area.
For example, you can develop this syndrome if you take migraine medicines called triptans together with antidepressants called selective serotonin reuptake inhibitors (SSRIs), or selective serotonin/norepinephrine reuptake inhibitors (SSNRIs).
Migraine
A migraine is a type of headache. It may occur with symptoms such as nausea, vomiting, or sensitivity to light and sound. In most people, a throbbi...
Read Article Now Book Mark ArticleCommon SSRIs include:
- Citalopram (Celexa)
- Escitalopram (Lexapro)
- Fluoxetine (Prozac)
- Paroxetine (Paxil)
- Sertraline (Zoloft)
SSNRIs include:
- Desvenlafaxine (Pristiq)
- Duloxetine (Cymbalta)
- Levomilnacipran (Fetzima)
- Milnacipran (Savella)
- Venlafaxine (Effexor)
Common triptans include:
- Almotriptan (Axert)
- Eletriptan (Relpax)
- Frovatriptan (Frova)
- Naratriptan (Amerge)
- Rizatriptan (Maxalt)
- Sumatriptan (Imitrex)
- Zolmitriptan (Zomig)
If you take these medicines, be sure to read the warning on the packaging. It tells you about the potential risk of SS. However, do not stop taking your medicine. Talk to your health care provider about your concerns first.
SS is more likely to occur when you first start taking or increase the dose of the medicine..
Older antidepressants called monoamine oxidase inhibitors (MAOIs) can also cause SS when combined with the medicines described above, as well as meperidine (Demerol, a painkiller), fentanyl, dextromethorphan (cough medicine), and others.
Street drugs, such as methamphetamine or other amphetamines, cocaine, opiates, ecstasy, LSD, and others have also been associated with SS.
Amphetamines
Amphetamines are drugs. They can be legal or illegal. They are legal when they are prescribed by a health care provider and used to treat health pr...
Read Article Now Book Mark ArticleCocaine
Cocaine is made from the leaves of the coca plant. Cocaine comes as a white powder, which can be dissolved in water. It is available as a powder or...
Read Article Now Book Mark ArticleLSD
LSD stands for lysergic acid diethylamide. It is an illegal street drug that comes as a white powder or clear colorless liquid. It is available in ...
Read Article Now Book Mark ArticleSymptoms
Symptoms occur within minutes to hours of taking medicines that can cause SS, and may include:
- Agitation or restlessness
- Abnormal eye movements
- Diarrhea
- Fast heartbeat and high blood pressure
- Hallucinations
- Increased body temperature
- Loss of coordination
Loss of coordination
Uncoordinated movement is due to a muscle control problem that causes an inability to coordinate movements. It leads to a jerky, unsteady, to-and-fr...
Read Article Now Book Mark Article - Nausea and vomiting
- Overactive reflexes
- Rapid changes in blood pressure
Exams and Tests
The diagnosis is usually made by asking the person questions about medical history, including the types of medicines they take.
To be diagnosed with SS, the person must have been taking a drug that changes the body's serotonin level (serotonergic drug) and have at least three of the following signs or symptoms:
- Agitation
Agitation
Agitation is an unpleasant state of extreme arousal. An agitated person may feel stirred up, excited, tense, confused, or irritable.
Read Article Now Book Mark Article - Abnormal eye movements called 'ocular clonus'
- Heavy sweating not due to activity
- Fever
- Mental status changes, such as confusion or hypomania
Confusion
Confusion is the inability to think as clearly or quickly as you normally do. You may feel disoriented and have difficulty paying attention, remembe...
Read Article Now Book Mark Article - Muscle spasms (myoclonus)
- Overactive reflexes (hyperreflexia)
Hyperreflexia
Autonomic dysreflexia (AD) is an abnormal, overreaction of the involuntary (autonomic) nervous system to stimulation. This reaction may include: Cha...
Read Article Now Book Mark Article - Shivering
- Tremor
- Uncoordinated movements (ataxia)
SS is not diagnosed until all other likely causes have been ruled out. This may include infections, intoxication, metabolic and hormone problems, and drug or alcohol withdrawal. Some symptoms of SS can mimic those due to an overdose of cocaine, lithium, or an MAOI.
If a person has just started taking or increased the dosage of a tranquilizer (neuroleptic drug), other conditions such as neuroleptic malignant syndrome (NMS) will be considered.
Tests may include:
- Blood cultures (to check for infection)
- Complete blood count (CBC)
Complete blood count
A complete blood count (CBC) test measures the following:The number of white blood cells (WBC count)The number of red blood cells (RBC count)The numb...
Read Article Now Book Mark Article - CT scan of the brain
CT scan of the brain
A head computed tomography (CT) scan uses many x-rays to create pictures of the head, including the skull, brain, eye sockets, and sinuses.
Read Article Now Book Mark Article - Drug (toxicology) and alcohol screen
Drug (toxicology) and alcohol screen
A toxicology screen refers to various tests that determine the type and approximate amount of legal and illegal drugs a person has taken by measuring...
Read Article Now Book Mark Article - Electrolyte levels
Electrolyte levels
Electrolytes are minerals in your blood and other body fluids that carry an electric charge. Electrolytes affect how your body functions in many ways...
Read Article Now Book Mark Article - Electrocardiogram (ECG)
Electrocardiogram (ECG)
An electrocardiogram (ECG) is a test that records the electrical activity of the heart.
Read Article Now Book Mark Article - Kidney and liver function tests
- Thyroid function tests
Thyroid function tests
Thyroid function tests are used to check whether your thyroid is working normally. The most common thyroid function tests are:Free T4 (free thyroxine...
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Treatment
People with SS will usually stay in the hospital for at least 24 hours for close observation.
Treatment may include:
- Benzodiazepine medicines to decrease agitation, seizure-like movements, and muscle stiffness
- Cyproheptadine (Periactin), a drug that blocks serotonin production
- Intravenous (through the vein) fluids
- Stopping medicines that caused the syndrome
In life-threatening cases, medicines that keep the muscles still (paralyze them), and a temporary breathing tube and breathing machine will be needed to prevent further muscle damage.
Outlook (Prognosis)
People may get slowly worse and can become severely ill if not quickly treated. Untreated, SS can be deadly. With treatment, symptoms usually go away in less than 24 hours. Permanent organ damage may result, even with treatment.
Possible Complications
Uncontrolled muscle spasms can cause severe muscle breakdown. The products produced when the muscles break down are released into the blood and eventually go through the kidneys. This can cause severe kidney damage if not recognized and treated properly.
When to Contact a Medical Professional
Contact your provider right away if you have symptoms of SS.
Prevention
Always tell your providers which medicines you take. People who take triptans with SSRIs or SSNRIs should be closely followed, especially right after starting a medicine or increasing its dosage.
References
Levine MD, Ruha AM. Antidepressants. In: Walls RM, eds. Rosen's Emergency Medicine: Concepts and Clinical Practice. 10th ed. Philadelphia, PA: Elsevier; 2023:chap 141.
Meehan TJ. Care of the poisoned patient. In: Walls RM, eds. Rosen's Emergency Medicine: Concepts and Clinical Practice. 10th ed. Philadelphia, PA: Elsevier; 2023:chap 135.
Praschan N, Beach SR, Fricchione GL, Huffman JC, Stern TA. Catatonia, neuroleptic malignant syndrome, and serotonin syndrome. In: Stern TA, Wilens TE, Fava M, eds. Massachusetts General Hospital Comprehensive Clinical Psychiatry. 3rd ed. Philadelphia, PA: Elsevier; 2025:chap 38.
Review Date: 4/3/2024
Reviewed By: Jesse Borke, MD, CPE, FAAEM, FACEP, Attending Physician at Kaiser Permanente, Orange County, CA. Also reviewed by David C. Dugdale, MD, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.