Headache Provocation of People Who Are Unable to Have Headache

Headaches are extremely common illnesses with a combined lifetime prevalence of 90-99% in Europe. Despite this high prevalence, there are persons who have never, in their whole life, encountered a headache. The aim of the study is to identify factors that protect against headache by studying headache after provocation in people who never have had a headache (headache resistant) versus non-resistant controls. The investigators will use isosorbide mononitrate as a pharmacological trigger of headache. The provocation is performed by investigators who are blinded to the grouping of the participants. The investigators hope to contribute with novelty to the current understanding of headache pathophysiology and development of more efficient treatment of headache.