Chronic Migraine (CM), or 15 or more migraine headaches per month, is common in tertiary headache care and is associated with a number of deleterious outcomes, especially higher disability and poorer quality of life, relative to those with Episodic Migraine (EM) defined as 14 or fewer migraine headaches per month. Limited work has begun to examine factors that increase or decrease the risk of developing CM. One factor that appears especially relevant is symptomatic medication use. The current study builds upon and expands previous work considering the influence non-steroidal anti-inflammatory drug (NSAID) and/or triptan use has on the likelihood of developing CM.

This study is a retrospective observational cohort study of data collected via mail survey and collated in the American Migraine Prevalence and Prevention (AMPP) database.

Survey results from the AMPP study will be analyzed retrospectively. The AMPP is a longitudinal, population-based, mailed-questionnaire survey. In 2004, 120,000 United States (US) households were screened and 24,000 individuals who reported severe headaches were identified and additional questionnaires have been administered annually. This analysis uses data from respondents who meet second edition of the International Headache Classification-2 (IHCD-2) criteria for EM in 2005 with follow up results in 2006, 2007, 2008, and 2009. EM is defined as 1 to 14 headaches per month and CM is defined as 15 or more headaches per month.

Inclusion Criteria:

• Respondents age 18 or older at the time of survey completion
• Respondents completed the questionnaires in 2004 and at least one other year (2005, 2006, 2007, 2008, 2009)
• Based on the respondents answers to the 2004 survey, their symptoms meet the criteria for EM which is characterized by headaches meeting International Classification of Headache Disorders - 2 (ICHD-2) criteria for migraine 1-14 days a month

Exclusion Criteria:

• Responses to questions suggest that the respondent's diagnosis is not migraine or CM

The American Migraine Prevalence and Prevention (AMPP) study is a multi-year longitudinal population-based study that follows a cohort of headache sufferers with severe headaches. From 2004 to 2009, respondents with headaches completed mailed questionnaires. Respondents had been screened from 120,000 US households and 24,000 individuals with severe headaches were invited to respond to annual questionnaires. Within the 2005 EM cohort a transition was defined to have occurred if in the observed year a respondent was CM and in the year immediately preceding that year a subject was EM. Participants were followed for up to 4 years with the provision that the individual provided data in 2005 and then in at least one subsequent year (2006-2009).