Sir Mir & Taylor (Psychiatric Bulletin, 23, 742-747) make an error in their article on serotonin syndrome. They start their article by stating that serotonin syndrome appears to be a new phenomenon; this is untrue. Serotonin syndrome is well-known to be an element of the carcinoid syndrome, a medical disorder characterised by high levels of circulating catecholamines due to inappropriate secretion by a tumour, for example, of the gut or adrenal medulla. This is not a drug side-effect.

The implications of this are potentially serious; a patient could present with the symptoms described without having a drug-induced serotonin syndrome, and the differential diagnosis is not discussed in this paper. The sections on ‘Causes of serotonin syndrome’ and ‘Biochemical mechanism of serotonin syndrome’ are, therefore, dangerously misleading. This could result in missed diagnoses of carcinoid syndrome, or misattribution of systemic serotonergic effects because other causes have not been considered.