Background: Maintenance of effect following treatment with galcanezumab compared to placebo in adult patients with episodic or chronic migraine was evaluated.Methods: In 2 similarly designed studies of patients with episodic migraine (6months) and 1 study of patients with chronic migraine (3months), patients randomized in a 1:1:2 ratio received a subcutaneous injection of galcanezumab 120mg/month (after an initial loading dose of 240mg) or 240mg/month or placebo. Maintenance of effect during the double-blind phase was evaluated based on a comparison of the percentages of galcanezumab- and placebo-treated patients with maintenance of 30, 50, 75, and 100% response (defined as 30, 50, 75, and 100% reduction from baseline in monthly migraine headache days [MHD]) at an individual patient level. Logistic regression analyses were used for between treatment comparisons. Results: A total of 1773 adult patients with episodic migraine (n=444 for galcanezumab 120mg;n=435 for galcanezumab 240mg;n=894 for placebo for 2 studies pooled) and 1113 patients with chronic migraine (n=278 for galcanezumab 120mg;n=277 for galcanezumab 240mg;n=558 for placebo) were evaluated. In patients with episodic migraine, 50% response was maintained in 41.5 and 41.1% of galcanezumab-treated patients (120mg and 240mg, respectively) for 3 consecutive months (until patient's endpoint) and 19.0 and 20.5%, respectively, for 6 consecutive months and was significantly greater than the 21.4 and 8.0% of placebo-treated patients at 3 and 6months consecutively (P<0.001). Approximately 6% of galcanezumab-treated patients maintained 75% response all 6months versus 2% of placebo-treated patients. Few galcanezumab-treated patients maintained 100% response. In patients with chronic migraine, 29% of galcanezumab-treated patients maintained 30% response all 3months compared to 16% of placebo patients while 50% response was maintained in 16.8 and 14.6% of galcanezumab-treated patients (120mg and 240mg) and was greater than placebo (6.3%;p<0.001). Few patients maintained 75% response. Conclusions: Treatment with galcanezumab 120mg or 240mg demonstrated statistically significant and clinically meaningful persistence of effect in patients with episodic migraine (3 and 6 consecutive months) and in patients with chronic migraine (for 3months).Study identification and trial registrationStudy Identification: EVOLVE-1 (I5Q-MC-CGAG);EVOLVE-2 (I5Q-MC-CGAH);REGAIN (I5Q-MC-CGAI)Trial RegistrationClinicalTrials.gov;NCT02614183 (EVOLVE-1);NCT02614196 (EVOLVE-2);NCT02614261 (REGAIN)