Background: Eptinezumab is approved in the US for migraine prevention. We demonstrate the consistency in migraine reduction from Day 1 across 4 weeks in patients with episodic (EM) or chronic migraine (CM) treated with eptinezumab. Methods: Four double-blind, placebo-controlled, randomized trials evaluated eptinezumab for migraine prevention: NCT01772524 (EM); NCT02559895 (EM, PROMISE-1); NCT02275117 (CM); NCT02974153 (CM, PROMISE-2). The percentage of patients experiencing migraine was evaluated on Day 1, then as an averaged daily occurrence weekly through Wk4; baseline was averaged over the 28-day screening period. Results: Approximately 31% of EM patients experienced migraine on any given day during baseline. PROMISE-1 percentages of patients with migraine on Day 1: 14.8% (100mg), 13.9% (300mg), 22.5% (placebo); during Wk4: 17.1%, 15.8%, 20.5%. NCT01772524 on Day 1: 4.8% (1000mg), 13.7% (placebo); during Wk4: 10.0%, 17.6%. Approximately 58-59% of CM patients experienced migraine on any given day during baseline. PROMISE-2 percentages on Day 1: 28.6% (100mg), 27.8% (300mg), 42.3% (placebo); during Wk4: 31.8%, 28.8%, 36.0%. NCT02275117 on Day 1: 29.3% (100mg), 26.5% (300mg), 48.7% (placebo); during Wk4: 30.2%, 30.1%, 41.0%. Conclusions: Across 4 migraine prevention trials, eptinezumab consistently demonstrated rapid onset of migraine preventive benefit, beginning Day 1 after initial treatment and sustained through ≥4 weeks.