Oxidative stress is one of the main mechanisms causing harm in severe infection with septic shock, ischemia-reperfusion injury in resuscitated cardiac arrest and ischemic and hemorrhagic stroke.

Melatonin is a potent scavenger of the mediators of oxidative stress, oxygen and nitrogen-reactive species, which directly injure cell structures like walls and DNA and thus cause organ dysfunction.

In a previous study we have observed that high-dose oral bedtime melatonin (OBM) is associated with improved organ function in severe Covid-19 patients

This is a double-blind randomized, adaptive trial in the 4 indications mentioned above giving 100 mg of OBM or placebo.

Interim analyses with pre-specified stopping rules will be performed in each sub-study for specific outcome variables collected at scheduled timelines.

Comparative organ dysfunction score (Sequential Organ Failure Evaluation-SOFA) will be done at baseline, 7, 14, and 30 days and mortality evaluated at 30 and 90 days.

For the 3 study groups enrolling stroke and resuscitated cardiac arrest patients, the modified Rankin score and the CVC (Glasgow) at 30 and 90 days will be compared.

Inclusion Criteria:

• ICU stay >5 days

Exclusion Criteria:

• ominous prognosis

Indistinguishable oral suspension or capsule