A Study of a Melatonin Receptor Agonist to Prevent Migraine

Inclusion Criteria: * Male or female, ages 18 to 65 years, inclusive. * An established history of migraine, with or without aura and probable migraine, conforming to the revised IHS criteria (2004) for at least 1 year before screening, sufficient to establish the diagnosis. * To be randomized, during the prospective 4-week baseline period (approximately 28 days before Visit 2), subjects must have more than 4 migraine/probable migraine attacks per month (using the 24-hour rule). * Must have been less than 50 years of age at the time of initial migraine onset. * Must have no clinically significant and relevant abnormalities on physical or neurologic examinations * Must have completed a washout of all prophylactic medications for migraine before the start of the 4-week prospective baseline period (ie, 28 days before Visit 2, when randomization occurs). * Female subjects must be at least 1 of the following: * postmenopausal, or * surgically incapable of being children, or * practicing a highly effective method of birth control Exclusion Criteria: * Most frequent type of headache does not meet the revised IHS diagnostic criteria for migraine with aura or without aura or probable migraine. * Pregnant or lactating women, or sexually active women of childbearing potential who are not using an appropriate method of contraception. * Failed adequate trials of prophylactic agents with demonstrated or possible efficacy in the prophylaxis of migraine. These agents include beta-blockers, tricyclic antidepressants, valproate, topiramate, and methysergide. * Unable to complete the diary in a timely and accurate manner after each migraine headache attacks, either independently or with assistance. * Overuse of analgesics or specific agents for abortive treatment of migraine attacks, which makes the investigator suspect medication overuse headache. * Receiving non-pharmacological prophylactic treatments such as acupuncture, chiropractic, or massage, if these were started less than 1 month before the screening visit (Day -28). These therapies may be continued if started before that time. * Currently abusing alcohol or other drugs. * Have a central nervous system neoplasm or infection, demyelinating disease, degenerative or progressive central nervous system disease, or active epilepsy. * History of serious systemic disease, including hepatic insufficiency, renal insufficiency, a malignant neoplasm, any disorder in which prognosis for survival is less than 3 months, or any disorder which in the judgment of the investigator will place the subject at excessive risk by participation in a controlled trial. * Have a significant psychiatric disorder, such as acute psychosis, schizophrenia, severe bipolar disorder, or severe unipolar mood disorder, of sufficient severity to preclude safe and effective participation of the subject in the study. * Require continued use of any of protocol-defined prohibited medications during the study * Have any recent or remote history of suicide attempt or ideation * Known or strongly suspected to be non-compliant in administering daily medications. * Received an experimental drug or used an experimental device within 30 days before the Screening Visit. * Employees of the investigator or study center, with direct involvement in the proposed study or other studies under the direction of that investigator or study center, as well as family members of the employees or the investigator * Any reason for which the investigator, upon her evaluation, feels that it is in the subject's best interest not to continue on in the study.