Duration of Benefit for OnabotulinumtoxinA in Treatment of Chronic Migraine

Inclusion Criteria: * male or female 18 years or older. * able to read, understand, and sign the informed consent. * a negative urine pregnancy test at visit 1, if female, and of childbearing potential. Note: If female of childbearing potential, subject must agree to maintain true abstinence or use one of the listed methods of birth control for the duration of the study: hormonal contraceptive, intrauterine device (IUD), condoms, diaphragm, and/or have a male partner who has undergone a successful vasectomy. The use of barrier contraceptive (condom or diaphragm) should always be supplemented with the use of a spermicide. Note: To be considered not of childbearing potential, subject must be 6 weeks post-surgical bilateral oophorectomy, hysterectomy, bilateral tubal ligation, postmenopausal for at least one year. * at least a one year history of migraine * history of chronic migraine (with or without aura) according to the criteria of the International Classification of Headache Disorders (ICHD)-3 for at least 3 months prior to enrollment (Appendix I) * able to differentiate migraine headache from any other headache they may experience (e.g., cluster headache) * onset of migraine before age 50 * willing to provide responses to questionnaires and complete the online diary. * if taking migraine preventive(s), be on a stable dose of the preventive medication for at least 30 days prior to screening * concomitant medication dosages approved by the investigator * email and internet access for completion of online diary Exclusion Criteria: * previously used onabotulinumtoxinA as a migraine preventative or has used onabotulinumtoxinA for any other reason during the prior year * female who is pregnant, planning to become pregnant during the study period, breast feeding, or is of childbearing potential and not practicing a reliable form of birth control * headache disorders outside ICHD-3 defined chronic migraine that cannot be easily distinguished from CM (Appendix I) * evidence of underlying pathology contributing to their headaches * any medical condition that may increase their risk with exposure to BTX including diagnosed myasthenia gravis, Eaton-Lambert syndrome, amyotrophic lateral sclerosis, or any other significant disease that might interfere with neuromuscular function * profound atrophy or weakness of muscles in the target areas of injection * skin conditions or infections at any of the injection sites * allergy or sensitivities to any component of the tes…