Study of Gammacore Sapphire for the Acute and Preventive Treatment of Post-Traumatic Headache (GAP-PTH)

Inclusion Criteria: 1. Meets the ICHD-3 criteria for acute headache attributed to mild traumatic injury to the head 2. Experiences a minimum of 2 headaches (migraine or probable migraine phenotype) per week 3. Presentation to clinic between 2 and 4 weeks after injury 4. Able to provide written informed consent Exclusion Criteria: 1. Any pre-existing primary headache disorder (with the exception of infrequent episodic tension type headache) 2. Any contraindication to using nVNS 3. Initiation or change in the dosage of any medication commonly used or headache prophylaxis 3 months before enrollment into the study 4. Continuous headache at the time of enrollment 5. PTH \>4 weeks after injury 6. Structural abnormality at the nVNS treatment site (e.g., lymphadenopathy, previous surgery, abnormal anatomy) 7. Pain at the nVNS treatment site (e.g., dysesthesia, neuralgia, cervicalgia) 8. Other significant pain problem (e.g., cancer pain, fibromyalgia, other head or facial pain disorder) that, in the opinion of the Investigator, may confound the study assessments 9. Known or suspected severe cardiac disease (e.g., symptomatic coronary artery disease, prior myocardial infarction, congestive heart failure) or an abnormal baseline electrocardiogram (ECG) within the last year (e.g., second- or third-degree heart block, prolonged QT interval, atrial fibrillation, atrial flutter, history of ventricular tachycardia or ventricular fibrillation, clinically significant premature ventricular contraction) 10. Known or suspected cerebrovascular disease (e.g., prior stroke or transient ischemic attack, symptomatic carotid artery disease, prior carotid endarterectomy or other vascular neck surgery) 11. Previous cervical vagotomy 12. A relative of or an employee of the Investigator or the clinical study site 13. Previously used gammaCore