Background: In patients with migraine, overuse of acute medication, including migraine-specific medication (MSM) such as triptans and ergots, can lead to adverse health outcomes, including development of medication overuse headache. Here, we examined the effect of erenumab on reducing acute medication use, in particular MSM, in patients with episodic migraine (EM) and chronic migraine (CM). Methods: The current post-hoc analyses were based on data from the double-blind treatment phase (DBTP) of two erenumab studies, a pivotal EM (N = 955) and a pivotal CM (N = 667) trial, and their respective extensions. Patients were administered subcutaneous placebo or erenumab (70 or 140 mg) once monthly. Daily acute headache medication use (including MSM and non-MSM) was recorded using an electronic diary during a 4-week pretreatment baseline period until the end of the treatment period. Outcome measures included change in monthly acute headache medication days (HMD) in acute headache medication users at baseline, and changes in monthly MSM days (MSMD) in MSM users at baseline and non-MSMD in non-MSM users at baseline. Results: In total, 60 and 78 % of patients (all acute headache medication users) with EM and CM used MSM at baseline, respectively. For acute headache medication users, the change in mean monthly acute HMD over Months 4, 5 and 6 compared with the pre-DBTP was 1.5, 2.5, and 3.0 for placebo, erenumab 70 mg and 140 mg, respectively for the EM study. The respective change in monthly MSMD in MSM users was 0.5, 2.1 and 2.8, and in monthly non-MSMD in non-MSM users was 2.3, 2.6, and 2.7. In the acute headache medication users at baseline, the change in monthly acute HMD at Month 3 compared with pre-DBTP was 3.4, 5.5, and 6.5 for placebo, erenumab 70 mg and 140 mg, respectively for the CM study. The respective change in monthly MSMD in MSM users was 2.1, 4.5, and 5.4, and in monthly non-MSMD in non-MSM users was 5.9, 6.4, and 6.6. Reductions in MSMD versus placebo were sustained in the extension periods of both studies. Erenumab was also associated with a higher proportion of MSM users achieving ≥ 50 %, ≥ 75 and 100 % reduction from baseline in monthly MSMD versus placebo in both EM and CM. Conclusions: In both EM and CM, treatment with erenumab is associated with a significant and sustained reduction in the use of acute headache medication, in particular MSM. Trial registrations: NCT02456740; NCT02066415; NCT02174861.