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.
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.