The purpose of this study is to determine the feasibility of conducting a randomized controlled trial (RCT) with melatonin for treatment of delirium in critically ill adult patients. From a feasibility perspective, the investigators believe that the proposed design will achieve the minimum enrollment rate necessary to conduct a future RCT on a larger scale.

The prevalence of delirium is high in the intensive care unit (ICU), yet there is no pharmacological treatment that has been proven effective. The investigators hypothesize that melatonin, given on a daily basis at 21:00, will safely decrease the mean duration of a delirium episode in ICU patients. The current literature evaluating melatonin as a treatment for delirium is lacking, therefore more studies are needed.

It is estimated that an alteration of sleep pattern can be found in up to 75% of patients with delirium. This raises the hypothesis that prevention and treatment of sleep disorders could potentially improve delirium. Sleep and circadian rhythm disturbances are associated with low endogenous melatonin secretion and studies have shown that it also occurs in patients with delirium.

Thus, the objective is to conduct a phase II double blind, placebo-controlled randomized trial comparing melatonin 9 mg to placebo to evaluate the feasibility of a future large-scale RCT. Participants will be followed during their stay in the ICU and after their transfer on another unit up to a maximum of 14 days. Feasibility of the larger trial will mainly be based on enrollment rates.

Inclusion Criteria:

• Patients aged 18 years or older admitted to the intensive care unit;
• Anticipated ICU stay > 48 hours;
• ICDSC score greater than or equal to 4 for a maximum of 48 hours prior to randomization.

Exclusion Criteria:

• Known allergy or hypersensitivity to melatonin or to ingredients in ORA-BLEND SF®;
• Use of melatonin within 24 hours prior to randomization;
• Presence of severe structural brain injury (intracranial hemorrhage or traumatic brain injury), severe major neurocognitive disorder, advanced neurodegenerative disease or hepatic encephalopathy;
• Diagnosis of schizophrenia, bipolar affective disorder, psychotic depression, uremic encephalopathy or alcohol withdrawal;
• Presence of active seizures, coma, aphasia or severe intellectual disability;
• Limited short-term vital prognosis;
• Diagnosis of delirium prior to ICU admission;
• Pregnancy or breastfeeding;
• Absolute contraindication to receive enteral medication;
• Inability to understand or speak English or French;
• Total blindness.

All study personnel, care provider, patients and their families will remain blinded. Randomization will be performed by members of the Pharmacy Research Department.