Objective:

Three possibilities may explain headache and depression comorbidity: (a) headaches cause depression; (b) depression causes headaches; and (c) third variables cause both. Evidence supports all three possibilities. This study sought to examine which of these has the most support among a sample of people seeking psychological treatment. Method:

This was achieved firstly by establishing the order of onset of the most recent episode of headaches and depression, comparing these groups on headache severity, depression heritability, and exploratory variables, and asking participants open-ended questions. Thirty participants had been diagnosed with a primary headache disorder and major depressive disorder. The order of onset was assessed using the Life History Calendar, while depression heritability was estimated by probable depression in a parent. Results:

Although the order of onset was statistically random, it was more frequent for participants to state that depression caused headaches than the reverse. Most participants identified life events or circumstances as contributing to both conditions. Unusually intense headaches may be contributing to depression in the headaches first group, although headaches causing depression may be infrequent. Conclusions:

Successful headache treatment for individuals with major depressive disorder will most likely necessitate treatment of the comorbid depression. This study was limited by a small sample size.