Exogenous Melatonin in Postmenopausal Women with Insomnia

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).