Are Melatonin and its Agonist the Natural Solution for Prevention of Delirium in Critically Ill Patients? A Review of Current Studies

[Background]Delirium is a neuropsychiatric syndrome, which is a common complication at the intensive care unit (ICU). Delirium is a risk factor for increased duration of mechanical ventilation and increased time of stay at the ICU and death. Melatonin is a hormone produced and secreted by the pineal gland, that regulates circadian rhythm. The aim of this investigation was to demonstrate the effect of melatonin in controlling and improving delirium.[Methods]Available data from Pubmed, Scopus, Medline, EMBASE, the Cochrane central register of controlled trials, and Cochrane database systematic reviews were reviewed.[Results]Pathogenic pathways of delirium are unclear, yet many risk factors have been identified, including patient’s history, acute illness, environment, administered drugs, and neuronal pathway. Several studies have suggested that delirium could be caused by decreased tryptophan as a precursor to the neurotransmitters, including serotonin and melatonin. On the other hand, a few studies have described that abnormal melatonin metabolism could be one of the mechanisms of delirium.[Conclusion]Exogenous melatonin could improve circadian rhythm and prevent delirium, therefore melatonin supplementation could be used for improvement or control of delirium at the ICU.