The Effect of Nasal Carbon Dioxide in the Treatment of Moderate to Severe Migraine

This multi-center, double-blind, placebo-controlled, parallel group trial carbon dioxide in the treatment of moderate to severe migraine. At approximately 8 US sites, approximately 450 patients who meet the eligibility criteria will be randomized to active or placebo in a 1:1 ratio to ensure that 400 patients will treat at least one moderate to severe migraine with the study drug. Patients will be randomized to one of two treatment groups and be provided with either an active or placebo dispenser. All patients will administer study drug for 10 seconds to each nostril when experiencing a qualifying headache. Patients will assess their pain and other migraine-related symptoms in a patient diary. If a patient still has pain and/or any other symptoms after the initial dose then the patient may opt to take 3 more doses to treat the headache. Each patient's participation in the study may last up to 56 days or once the patient treats 4 headaches with the study drug, whichever occurs first. There will be a total of 2 scheduled clinic visits: * Visit 1 Screening/Randomization * Visit 2 End of Study (within 7 days after the patients treats his/her fourth headache or after the end of the 56-day treatment period, whichever occurs first)