Mixed state and suicide: Is the effect of mixed state on suicidal behavior more than the sum of its parts?

Objective To assess whether suicidal behavior during mixed states exceeds that expected from the manic or depressive components alone. Methods This study included 429 participants with bipolar disorder from the National Institute of Mental Health Collaborative Depression Study (CDS). Mood and suicidal behavior were captured using the Longitudinal Interval Follow-up Evaluation and the Schedule of Affective Disorders and Schizophrenia. Suicidal behavior during each mood state, relative to euthymia, was analyzed using Cox regression to allow for repeated events, with a frailty term to account for intra-participant correlation. Mixed states were modeled as a depression-by-mania interaction. Results Individuals with a history of mixed states were at higher risk of suicidal behavior and spent more time depressed, compared to subjects with no such history. In bipolar I disorder, risk increased during episodes of mania (hazard ratio [HR]: 1.96, 95% confidence interval [CI]: 1.28-2.99, P = .0019) and depression (HR: 5.49, 95% CI: 4.01-7.51, P < .0001) and there was a less than additive effect of mixed states. In bipolar II disorder, risk was increased during episodes of depression (HR: 3.66, 95% CI: 2.51-5.35, P < .0001) and there was no excess risk during mixed states beyond that attributable to the depressed component. Most of the excess risk (71%) among those with a history of mixed states was attributable to a depression predominant course of illness. Conclusions Individuals with mixed states are at high risk of suicidal behavior, largely due to more time spent depressed. Clinicians should aggressively treat depression to mitigate suicide risk for patients with or without mixed states.