Are migraine and bipolar disorders comorbid phenomena?: findings from a pharmacoepidemiological study using the Norwegian Prescription Database.

ABSTRACT

OBJECTIVES: Clinical, epidemiological, and, recently, genome-wide linkage and genome-wide association studies suggest migraine and bipolar disorder are comorbid phenomena. The objective of this study was to determine whether there is also evidence that this comorbidity exists by virtue of there being a positive relationship between the prescription of medications used to treat migraine and mood-stabilizing agents using the National Norwegian Prescription Database. METHODS: Data allowing ascertainment of the concurrence of prescriptions for migraine and mood-stabilizing agents were gleaned from the Norwegian Prescription Database for calendar year 2006, covering the total population (N = 4,640,219). Results were obtained using logistic regression analyses and were expressed by odds ratios (ORs). RESULTS: A total of 81,225 persons (1.8% of the population) received medications for migraine and 19,517 (0.45%) received a mood-stabilizing agent for a bipolar disorder; 843 persons received both types of medications. The OR expressing the relationship between the concurrent use of both categories of medications was 2.55 (95% confidence interval [CI], 2.38-2.73, P < 0.001, z score = 26.44), significant for all mood stabilizers (lithium OR = 1.82 [95% CI, 1.58-2.10], P < 0.001, z score = 8.31; carbamazepine OR = 2.48 [95% CI, 2.01-3.06], P < 0.001, z score = 8.42; valproic acid OR = 2.26 [95% CI, 1.89-2.70], P < 0.001, z score = 8.96; and lamotrigine OR = 3.50 [95% CI, 3.14-3.90], P < 0.001, z score = 22.68). The association was significantly higher for men (OR = 3.16 [95% CI, 2.74-3.66], P < 0.001, z score = 15.53) than for women (OR = 2.21 [95% CI, 2.04-2.39], P < 0.001, z score = 19.61) and was most pronounced in younger age groups and for lamotrigine. CONCLUSIONS: There was a strong positive association between the prescription of medications used to treat migraine and mood-stabilizing agents. This is compatible with the hypothesis that migraine and bipolar disorders are associated with one another.