Handy Fact Sheet: Serotonin Syndrome

Serotonin Syndrome

What’s the problem?

• Serotonin Syndrome is a rare side effect of some medicines.

• It happens when the brain has too much serotonin.

• It can cause confusion, fever, sickness, diarrhoea, or muscle twitches.

• If not treated quickly, it can become serious or even life-threatening.

How will I know if I have Serotonin Syndrome?

Watch out for these symptoms:

• Feeling confused, agitated, or restless

• Sweating, fever, shivering, or shaking

• Diarrhoea (“the runs”)

• Muscle twitches or jerks

• Fast heartbeat

• Feeling sick or vomiting

• In severe cases: seizures or fits

⚠️ Important: Symptoms can look like flu, infections, withdrawal effects, or even side effects from other medicines — but if you’re taking serotonin-boosting drugs, it’s safest to get checked quickly.

Why is it important?

• Most cases are mild, but some can be very dangerous.

• Getting help quickly can prevent serious illness.

What causes Serotonin Syndrome?

It usually happens:

• A few days after increasing the dose of a serotonin medicine

• When starting another medicine

• After an accidental overdose (e.g. double dose)

Medicines that can cause problems include:

• SSRIs and similar antidepressants: citalopram, escitalopram, fluoxetine (and up to 6 weeks after stopping), paroxetine, sertraline, venlafaxine, trazodone, duloxetine

• Tramadol and St. John’s Wort

• Tricyclic antidepressants (e.g. clomipramine)

• MAOIs (e.g. tranylcypromine)

• Linezolid (antibiotic)

• Opioids (e.g. buprenorphine)

• Illicit drugs: ecstasy, amphetamines

• Triptans for migraine: rare but possible risk when combined with SSRIs

What should I do if I think I have Serotonin Syndrome?

• Call your prescriber straight away if symptoms start.

• If you can’t reach them, go to A&E immediately.

• Always tell your prescriber if you’ve had suspected serotonin syndrome before.

• Take a copy of this fact sheet with you — not all healthcare staff will be familiar with it.

How is it treated?

Treatment depends on how severe it is:

1. Stop the medicine that boosts serotonin – often this is enough.

2. Treat the symptoms:

   • Cooling measures (fans, hydration)

   • Medicines such as lorazepam (to calm agitation)

   • Cyproheptadine (blocks serotonin effects)

✅ Key takeaway:
Know the symptoms. Get help quickly. Don’t ignore it.