Serotonin syndrome

Serotonin syndrome occurs when the level of a chemical in the brain, called serotonin, gets too high. It is a known adverse reaction associated with the use of some medicines or herbal supplements that increase serotonin.

On this page, you can find the following information:

Key points

  1. Serotonin is a chemical produced in the body. It is needed for nerve cell and brain function. 
  2. Serotonin syndrome occurs when the level of serotonin gets too high. This may be caused by the use of some medicines or herbal supplements that increase serotonin.
  3. Symptoms of serotonin syndrome can range from mild (shivering and diarrhoea) to severe (muscle rigidity, fever and seizures). 
  4. Milder forms of serotonin syndrome may go away within a few days of stopping the medicines that caused the symptoms. 
  5. Severe serotonin syndrome needs hospital admission and can be fatal if not treated.

What causes serotonin syndrome?

Serotonin syndrome is a known adverse reaction associated with the use of some medicines or herbal supplements.

The following are examples of medicines and herbal supplements known to increase serotonin levels: 

  • Selective Serotonin Reuptake Inhibitors (SSRIs) such as citalopram, escitalopram, fluoxetine, fluvoxamine, paroxetine, sertraline.
  • Tricyclic Antidepressants (TCAs) such as amitriptyline, imipramine, clomipramine, nortriptyline.
  • Serotonin-Noradrenaline Reuptake Inhibitors (SNRIs) such as venlafaxine, duloxetine.
  • Atypical Antidepressants such as mirtazipine.
  • Lithium or linezolid
  • Monoamine Oxidase Inhibitors (MAOIs) such as moclobemide, phenelzine, tranylcypromine.
  • Opioid Analgesics (pain medication) such as pethidine, fentanyl, tramadol.
  • Migraine medication such as sumitriptan, rizatriptan, zolmitriptan.
  • Nausea medication such as ondansetron, granisetron.
  • Cough suppressants such as dextromethorphan.
  • Herbal Products such as St John's Wort.

Some people are more sensitive to these medicines and supplements that cause serotonin syndrome than are others, but the condition can occur in anyone.

You are at increased risk of serotonin syndrome if:

  • You recently started taking or increased the dose or have taken too much of a medicine known to increase serotonin levels.
  • You take more than one medicine known to increase serotonin levels.
  • You take herbal supplements known to increase serotonin levels.
  • You use an illicit drug known to increase serotonin levels.

What are the symptoms of serotonin syndrome?

Serotonin syndrome symptoms usually occur within hours to days of taking the medicine or increasing the dose of a medicine you are already taking. Signs and symptoms include:

  • feeling agitated or restless
  • confusion
  • fast heart rate or irregular heart beat
  • loss of muscle coordination or twitching muscles
  • muscle rigidity
  • heavy sweating
  • diarrhoea
  • headache
  • shivering
  • goose bumps
  • high fever
  • seizures
  • unconsciousness.

How can I prevent serotonin syndrome?

Taking more than one medication known to increase serotonin levels increases your risk of serotonin syndrome. Talk to your doctor about possible risks.

  • Don't stop taking any such medications on your own.
  • If your doctor prescribes a new medication, make sure they know about all other medications you're taking, especially if you receive prescriptions from more than one doctor or if you are taking herbal medicines or illicit drugs.
  • If you and your doctor decide the benefits of combining certain drugs that affect serotonin levels outweigh the risks, be alert to the possibility of serotonin syndrome.

What is the treatment for serotonin syndrome?

The treatment for serotonin syndrome depends on the severity of your symptoms.

  • If your symptoms are mild, a visit to the doctor and stopping the medication causing the problem may be enough. In milder forms, symptoms of serotonin syndrome usually go away within 24 to 72 hours of stopping medications that increase serotonin.
  • If you have symptoms that concern your doctor, you may need to go to the hospital. Your doctor may have you stay in the hospital for several hours to make sure your symptoms are improving.
  • If you have severe serotonin syndrome, you'll need intensive treatment in a hospital.

Learn more

The following links have more information on serotonin syndrome.
Be aware that websites from other countries may contain information that differs from New Zealand recommendations.

Serotonin syndrome Medsafe, NZ
Serotonin Syndrome Patient Info, UK


Advice about serotonin syndrome Medsafe, NZ, 2015

Information for healthcare providers

Reminder – interactions resulting in serotonin syndrome Medsafe, NZ, 2015
Advice about serotonin syndrome Medsafe, NZ, 2015
Reminder – serotonin syndrome/toxicity  Medsafe, NZ, 2010

Reviewed by

Angela is a pharmacist in the Quality Use of Medicines Team at Waitematā District Health Board. She has experience in hospital pharmacy in New Zealand and in the UK, and was previously a medical writer for Elsevier in The Netherlands. Angela is interested in promoting the safe use of medicines, particularly high-risk medicines.
Credits: Sandra Ponen, Pharmacist. Reviewed By: Angela Lambie, Pharmacist, Auckland Last reviewed: 14 Feb 2019