Effect of Sildenafil in Individuals With Migraine Pretreated With Erenumab

Inclusion Criteria: * Participant has provided informed consent prior to initiation of any study-specific activities/procedures. * Age ≥18 years upon entry into screening. * History of migraine without aura for ≥12 months with a frequency of 1-5 migraine attacks per month before screening according to the International Headache Society (IHS) Classification ICHD-3 (Headache Classification Committee of the International Headache Society, 2018), based on medical records and/or patient self-report. Exclusion Criteria: * History of any primary headache disorder other than migraine without aura, or tension-type headache with a frequency of ≥5 headache days per month before screening according to the International Headache Society (IHS) Classification ICHD-3 (Headache Classification Committee of the International Headache Society, 2018), based on medical records and/or patient self-report. * History of any secondary headache disorder before screening according to the International Headache Society (IHS) Classification ICHD-3 (Headache Classification Committee of the International Headache Society, 2018) based on medical records and/or patient self-report. * Intake of prophylactic migraine medication within ≤30 days or 5 plasma half-lives (whichever is longer) prior to screening. * Prior intake of therapies targeting the CGRP signaling pathway, including anti-CGRP ligand monoclonal antibodies, anti-CGRP receptor monoclonal antibodies, and small molecule CGRP receptor antagonists. * The participant is at risk of self-harm or harm to others as evidenced by past suicidal behavior. * History or evidence of any other clinically significant disorder, condition, or disease (with the exception of those outlined above) that, in the opinion of the investigator will pose a risk to participant safety or interfere with the study evaluation, procedures or completion. * Female participants of childbearing potential with a positive pregnancy test assessed at screening or day 1 by a urine pregnancy test. * Female participants who are pregnant or breastfeeding or plan to become pregnant or breastfeed during participation in the study. * Evidence of current pregnancy or breastfeeding per participant self-report or medical records. * Participants likely to not be available to complete all protocol-required study visits or procedures, and/or to comply with all required study procedures to the best of the participants' and investigator's knowledge.