Causality and Headache Triggers


  • Conflicts of Interest: Dana P. Turner: unrestricted grant funding from Merck; Todd A. Smitherman: nothing to disclose; Vincent T. Martin: consultant and speaker with Allergan, consultant with Nautilus and Zogenix, and grant funding from GlaxoSmithKline; Donald B. Penzien: unrestricted grant funding from Merck; Timothy T. Houle: unrestricted grant funding from Merck, and consultant with Allergan.
  • Financial Support: Research reported in this publication was supported by the National Institute of Neurological Disorders and Stroke of the National Institutes of Health under award number 1R01NS06525701.

Address all correspondence to D.P. Turner, Department of Anesthesiology, Wake Forest School of Medicine, Winston-Salem, NC 27157, USA, email:



The objective of this study was to explore the conditions necessary to assign causal status to headache triggers.


The term “headache trigger” is commonly used to label any stimulus that is assumed to cause headaches. However, the assumptions required for determining if a given stimulus in fact has a causal-type relationship in eliciting headaches have not been explicated.


A synthesis and application of Rubin's Causal Model is applied to the context of headache causes. From this application, the conditions necessary to infer that 1 event (trigger) causes another (headache) are outlined using basic assumptions and examples from relevant literature.


Although many conditions must be satisfied for a causal attribution, 3 basic assumptions are identified for determining causality in headache triggers: (1) constancy of the sufferer, (2) constancy of the trigger effect, and (3) constancy of the trigger presentation. A valid evaluation of a potential trigger's effect can only be undertaken once these 3 basic assumptions are satisfied during formal or informal studies of headache triggers.


Evaluating these assumptions is extremely difficult or infeasible in clinical practice, and satisfying them during natural experimentation is unlikely. Researchers, practitioners, and headache sufferers are encouraged to avoid natural experimentation to determine the causal effects of headache triggers. Instead, formal experimental designs or retrospective diary studies using advanced statistical modeling techniques provide the best approaches to satisfy the required assumptions and inform causal statements about headache triggers.