Prevention of Delirium in Intensive Care by Melatonin

Inclusion Criteria: * Age ≥18 years * Patient under invasive mechanical ventilation * Anticipated stay in intensive care unit of at least 48 hours * Informed consent signed by the patient or a relative or emergency consent Exclusion Criteria: * Invasive mechanical ventilation for more than 48 hours * known pregnancy or breastfeeding * No understanding of the French language, deafness * Dementia (Mini Mental State \<20) or known chronic psychosis * Delirium (positive CAM-ICU score) before or at the time of randomization * Alcohol withdrawal syndrome before or at the time of randomization with Cushman score ≥5 * Inability to use the enteral route, food intolerance with vomiting * Severe hepatic insufficiency (prothrombin level \<30%) * Ongoing treatment with melatonin or a drug that interacts or modifies its metabolism (fluvoxamine, 5- or 8-methoxypsoralen, estrogen, cimetidine, carbamazepine, rifampicin) * known allergy to melatonin * moribund state * Patient admitted to intensive care for cardiopulmonary arrest, stroke, head trauma, neurosurgery. * Patient not affiliated to social security * Patient participating in another interventional clinical study with melatonin and / or for whom delirium is the primary endpoint