The serotonin syndrome is a complex of symptoms that are thought to be largely attributable to changes in sensitivity in the serotonin receptor systems in the brainstem and the spinal cord due to drugs. Severe cases are almost always caused by a combination of two or more 'serotonergic' drugs, of which at least one is a selective serotonin reuptake inhibitor or a monoamine oxidase inhibitor. Usually, the syndrome heals spontaneously after withdrawal of the medication. Cessation of 'serotonergic' medication is the preferred treatment as well as supportive care.