Serotonin syndrome (or hyperserotonemia) is a hyperserotonergic state, that is an excess of 5-HT (serotonin) in the central nervous system. It is usually associated with high doses of serotonergic drugs, when combinations of serotonergic agents are used together, or when antidepressants are changed without an adequate washout period between drugs.
Less frequently it can also be caused by moderate dosage of a single serotonergeric drug, or in combination with non-serotonergeric drugs such as oxycodone, erythromycin, or St. John’s Wort.
Serotonin syndrome is rare, but it is a serious, potentially life-threatening medical condition. However there is no lab test for the condition, so diagnosis is by symptom observation. It may go unrecognized because it is often mistaken for a viral illness, anxiety, neurological disorder or worsening psychiatric condition.
Clinicians must differentiate between serotonin syndrome and Neuroleptic malignant syndrome, which has similar symptoms. Patients taking serotonergic drugs and who have sudden onset of the below symptoms should immediately seek medical care.