What is serotonin syndrome?

Some medicines increase the amount of serotonin (a brain chemical called a neurotransmitter). Combining these medicines with other medicines or illegal drugs that also increase serotonin can cause a serious reaction called serotonin syndrome or serotonin toxicity. Avoid combinations of the medicines listed in the table below.

Symptoms of serotonin toxicity include:

  • confusion
  • sweating
  • unsteadiness
  • shaking
  • diarrhoea.

Severe cases of serotonin syndrome may be fatal. Get medical care urgently if you think you are having this reaction.

Medicines that increase the risk of serotonin toxicity

Do not take any of the medicines below together unless you are under careful medical supervision.

Category of medicine
Active ingredient (with some brand name examples)
All antidepressants, except reboxetine and agomelatine
Linezolid (e.g. Zyvox)
Complementary medicines
St John’s wort
Cough and cold medicines
Dextromethorphan (in many cough and cold medicines, e.g. Benadryl, Dimetapp)
Migraine medicines
Sumatriptan (e.g. Imigran, Sumagran, Sumatab, Suvalan)
Rizatriptan (e.g. Maxalt)
Naratriptan (e.g. Naramig)
Eletriptan (e.g. Relpax)
Zolmitriptan (e.g. Zomig)
Mood stabilisers
Lithium (e.g. Lithicarb, Quilonum)
Parkinson’s disease medicines

Selegiline (e.g. Eldepryl, Selgene)
Rasagiline (Azilect)

Strong pain medicines
Fentanyl (e.g. Actiq lozenge, Denpax patches, Durogesic patches)
Tramadol (e.g. Lodam capsules, Durotram, Tramal, Tramedo, Zydol)
Weight loss medicines
Phentermine (e.g. Duromine, Metermine)
Sibutramine (e.g. Ectiva, Reductil)
Buspirone (e.g. Buspar), for anxiety
Tryptophan (an amino acid)
Dexamphetamine, for ADHD or narcolepsy

Do not take any of the medicines in the table above if you are taking another medicine called a monoamine oxidase inhibitor (MAOI), and wait 14 days after stopping an MAOI before taking any of these medicines. Taking them with an MAOI or taking it too soon after stopping an MAOI may cause serotonin syndrome. MAOI medicines include:

  • phenelzine (Nardil), an antidepressant
  • tranylcypromine (Parnate), an antidepressant
  • selegiline (Eldepryl, Selgene), for Parkinson’s disease.

Read more about how medicine interactions can happen.

Antidepressants and illegal drugs don’t mix!

Taking illegal drugs such as ecstasy, cocaine, amphetamines (speed) or LSD (acid) with an antidepressant increases the risk of serotonin toxicity, which can be fatal. If you have a problem with drugs, you may benefit from counselling as this can help you recover from depression.