aMO was defined as use of acute headache medication on ≥ 15 days, migraine-specific acute medication on ≥ 10 days, or combination medication for headache on ≥ 10 days during the 28-day pretreatment period. bA headache day of at least moderate severity was defined as a calendar day in which headache pain lasted at least 4 consecutive hours and had a peak severity of at least a moderate level, or a day in which acute migraine-specific medication (triptan or ergot) was used to treat a headache of any severity or duration. cA migraine day was defined as a calendar day in which headache pain lasted at least 4 consecutive hours and met criteria for migraine (with or without aura) or probable migraine (subtype in which only one migraine criterion is absent), or a day in which acute migraine-specific medication (triptan or ergot) was used to treat a headache of any duration.