AIM: To evaluate the relationship between cognitive impairment and work productivity loss in patients with bipolar disorder. METHODS: We enrolled outpatients with bipolar disorder aged 18-59 years undergoing treatment and actively employed or on sick leave. Baseline demographic, medical resource use, and employment data were collected. We evaluated work productivity, cognitive impairment, quality of life (QOL), depressive symptoms (defined as a Patient Health Questionnaire-9 [PHQ-9] score of ≥ 10), and sleep disturbance. This interim analysis examined correlations among baseline symptom scores and correlations of each symptom score with work productivity loss and QOL. RESULTS: Among 211 participants, cognitive impairment was moderately correlated with depressive symptoms (r = 0.595) and insomnia (r = 0.481), and depressive symptoms and insomnia were highly correlated (r = 0.719) (all p <
0.001). Work productivity loss (presenteeism) was moderately correlated with cognitive impairment (r = 0.474), depression (r = 0.577), and insomnia (r = 0.547) (all p <
0.001). Depression had the strongest influence on presenteeism (multiple regression analysis, regression coefficient: 22.98
p <
0.001). Among participants without severe depressive symptoms (PHQ-9 ≤ 19), cognitive impairment (13.91, p = 0.007) and insomnia (13.80, p = 0.016) strongly affected presenteeism. Among participants without moderately severe or severe depressive symptoms (PHQ-9 ≤ 14), insomnia affected presenteeism (23.14, p = 0.011). QOL was moderately negatively associated with cognitive impairment (r = -0.653), depression (r = -0.699), and insomnia (r = -0.559) (all p <
0.001). In multiple regression analysis, cognitive impairment (-0.12, p <
0.001), depression (-0.12, p = 0.010), and insomnia (-0.16, p <
0.001) were significantly associated with QOL. CONCLUSIONS: Treatment should focus on improving the core symptoms of bipolar disorder, insomnia, and cognitive impairment. TRIAL REGISTRATION: UMIN Clinical Trials Registry (UMIN000051519).