Lack of funding

The aim of the study is to assess the effect of exogenous melatonin, 2 mg SR, 60 minutes before bedtime for 15 days, on the sleep and circadian rhythms of postmenopausal women with insomnia in a randomized crossover placebo-controlled study.

Eligible participants will be contacted by the research team to provide informed consent for the study. Once the screening phase is completed, they will be ready to start the study consisting of:

A) a ~2-week ambulatory phase at home with melatonin or placebo treatment; B) a 2-week wash-out period; C) same as A with the opposite treatment;

Part A: The research project will start with a 16-day ambulatory data-collection period during which participants will receive either melatonin or a placebo. They will take 2 mg of exogenous melatonin in a slow release formulation (or placebo), 60 mins prior to bedtime for 15 days. Participants will be instructed to go to bed at a regular time and stay in darkness for 8 consecutive hours each night, trying to sleep.

Part B: Throughout this period, all participants will stop taking their melatonin/placebo pills. After at least 2 weeks, they will prepare to participate to the other study condition.

Parts C: Repetition of Ambulatory phase 1 (Part A) except that participants who received the active treatment will now receive placebo and vice versa.

Inclusion Criteria:

• Insomniac women will meet the diagnostic criteria for persistent insomnia as described in the Diagnostic and Statistical Manual of Mental Disorders, 5th Edition (DSM-5). They will report subjective sleep onset and/or maintenance difficulties associated with impaired daytime functioning at least 3 times a week, for at least 3 months. Sleep disturbances will be coincident with the onset of the menopausal transition.
• Postmenopausal women will have amenorrhea for at least 12 months.
• Participants will be drug-free at the time of study, and will have a history of only moderate or no use of coffee (≤3 cups/day), tobacco (≤ 10 cigarettes/day), alcohol (≤ 15 drinks/week), or other compounds.

Exclusion Criteria:

• Evidence of psychopathology on the Structured Clinical Interview for DSM-5, the Seasonal Pattern Assessment Questionnaire, the Beck Depression Inventory, and the Spielberger State Trait Anxiety Inventory.
• A history of prior gynecological pathology or medical condition that can affect the study results, including bilateral oophorectomy or endocrinopathy, and will not have used investigational drugs within 4 weeks of the study.
• A history of night work or transmeridian travel (across >2 time zones) in the 2 months prior to the study.
• Evidence of sleep apnea (apnea/hypopnea index > 15 per hour of sleep) or restless legs, or periodic limb movements during sleep (number of PLMs >15 per hour of sleep).

The nature of the treatment (melatonin vs placebo) will only be unrevealed when the key parameters have been determined (e.g, PSG sleep scoring, alertness levels, vasomotor symptoms, adverse effects, hormone levels).