VIP and Headache: A study in patients found that infusion of VIP led to dilation of cranial arteries but could not elicit migraine or headaches.43 Recent developments, on the other hand, suggest VIP is relevant in headache,44 including a recent small clinical study in which longer infusions of VIP (2 h) resulted in headaches in some patients.45 However, due to the recent nature of these VIP migraine studies it was not included in our model.