Residual insomnia is associated with a risk of depression recurrence.
In this retrospective, longitudinal cohort study, the recurrence pattern of depression in patients with or without residual insomnia was assessed using a health insurance claims database. Patients who were diagnosed with major depressive disorder and prescribed antidepressants, between January 2006 and June 2017 in Japan, were enrolled in the study. Residual insomnia was defined by a prescription of hypnotics, and recurrence of depression by prescription of antidepressants. Main outcomes included time to recurrence and the 1-year recurrence rate. Factors associated with recurrence of depression were assessed by multivariate analyses. The effect of residual insomnia on the frequency of recurrence was assessed by Chi-square test.
Of the 30,381 patients analyzed, there were 4,166 and 26,215 patients with or without residual insomnia, respectively. Time to recurrence in patients with residual insomnia was significantly shorter compared with those without residual insomnia (p <0.001), with a 1-year recurrence rate (95% CI) of 43.4% (41.9-45.0) and 7.4% (7.1-7.7), respectively. The frequency of recurrence was significantly higher in patients with residual insomnia than in those without (p <0.0001). A higher risk of depression recurrence (odds ratio 9.98, 95% CI 9.22-10.81) was found for residual insomnia compared with other significant factors.
The diagnosis stated in the receipt data may not accurately reflect the patient’s condition, and medication adherence was unknown but assumed.
Residual insomnia is a significant risk factor for depression recurrence in Japanese patients.

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