The goal of this clinical trial is to evaluate whether the timing and dosage of exogenous melatonin can improve sleep onset and maintenance in healthy adults aged 18-45 years (50% female) with no history of sleep disorders.

The main questions it aims to answer is whether an optimized melatonin administration schedule (4 mg, 3 hours before bedtime) will be more effective in improving sleep initiation and maintenance than an administration schedule more commonly advised (2 mg, 30 minutes before bedtime).

Researchers will compare five conditions involving different combinations of melatonin or placebo administered 30 minutes or 3 hours before bedtime to see if earlier timing and/or higher dosage produces better sleep outcomes.

Participants will:

• Complete a habituation night without any intervention.

• Undergo five randomized, double-blind experimental sleep conditions including:

  2 mg melatonin 30 minutes before bedtime 2 mg melatonin 3 hours before bedtime 4 mg melatonin 30 minutes before bedtime 4 mg melatonin 3 hours before bedtime Placebo at both time points

• Be monitored via polysomnography to measure sleep parameters

Inclusion Criteria:

• Age between 18 and 45 years of age
• Fluent knowledge of Italian language
• Review and signing of the informed consent form

Exclusion Criteria:

• Diagnosis of sleep or circadian rhythm disorder
• Diagnosis of neurological, psychiatric or medical condition that may interfere with sleep
• Ongoing treatment with medications that may affect sleep, including hypnotics and other types of melatonin
• Travel to a country with a time zone difference of at least two hours within the two months prior to or during the study
• Shift work
• Confirmed pregnancy
• Breastfeeding

The data cannot be shared publicly for the privacy of individuals who participated in the study