Inclusion Criteria:

• Males or females aged 18 to 65 years of age.
• A signed and dated informed consent document indicating that the subject has been informed of all pertinent aspects of the study including any known and potential risks and available alternative treatments.
• Subjects fulfilling criteria for episodic migraine as per the Second Edition of The International Headache Society (Olesen and Steiner 2004), who experience migraine at high frequency as follows:
  • History of headaches on more than 8 days per month for at least 3 months prior to screening
  • Verification of headache frequency through prospectively collected baseline information during the 28-day run-in phase demonstrating headaches (of any type) on at least 8 days with at total of 8 to 14 days* fulfilling criteria for migraine.
    *Operational definition for migraine and probable migraine days are presented in the statistical section of this protocol.
• Body Mass Index (BMI) of 17.5 to 37.5 kg/m2, and a total body weight between 50 kg and 120 kg, inclusive.
• Demonstrated compliance with the electronic headache diary during the run-in period by entry of headache data on a minimum of 22/28 days (80% compliance).

Exclusion Criteria:

• Subject has received onabotulinum toxin A for migraine or for any medical or cosmetic reasons requiring injections in the head, face, or neck during the six months prior to screening.
• Subject uses medications containing opioids (including codeine) or barbiturates (including Fiorinal®, Fioricet®, or any other combination containing butalbital) on more than 4 days per month for the treatment of migraine or for any other reason.
• Failed > 2 medication categories or > 3 preventive medications (within two medication categories) due to lack of efficacy for prophylactic treatment of episodic or chronic migraine after an adequate therapeutic trial
• Treatment with an investigational drug or device within 30 days of study entry or any prior exposure to a monoclonal antibody targeting the CGRP pathway.