Causes

• monoamine oxidase inhibitors
• SSRIs
  • St John's Wort, often taken over the counter for depression, can interact with SSRIs to cause serotonin syndrome
  • tramadol may also interact with SSRIs
• ecstasy
• amphetamines

Features

• neuromuscular excitation
  • hyperreflexia
  • myoclonus
  • rigidity
• autonomic nervous system excitation
  • hyperthermia
  • sweating
• altered mental state
  • confusion

Management

• supportive including IV fluids
• benzodiazepines
• more severe cases are managed using serotonin antagonists such as cyproheptadine and chlorpromazine

Venn diagram showing contrasting serotonin syndrome with neuroleptic malignant syndrome. Note that both conditions can cause a raised creatine kinase (CK) but it tends to be more associated with NMS.