Recovery from multiple episodes of bipolar I depression.

Objective: To describe the duration of bipolar I major and minor depressive episodes and factors associated with time to recovery.

Method: As part of the National Institute of Mental Health Collaborative Depression Study, 219 participants with bipolar I disorder based on Research Diagnostic Criteria analogs to DSM-IV-TR criteria were recruited at 5 academic medical centers from 1978 to 1981 and followed for up to 25 years with the Longitudinal Interval Follow-Up Evaluation. The probability of recovery over time from depressive episodes, the primary outcome measure, was examined with mixed-effects grouped-time survival models.

Results: The median duration of major depressive episodes was 14 weeks, and over 70% of participants recovered within 12 months of episode onset. The median duration of minor depressive episodes was 8 weeks, and approximately 90% of participants recovered within 6 months of onset of the episode. Aggregated data demonstrated similar durations of the first 3 major depressive episodes. However, for each participant with multiple episodes of major depression or minor depression, the duration of each episode was not consistent (intraclass correlation coefficient = 0.07 and 0.25 for major and minor depression, respectively). The total number of years in episode over follow-up with major plus minor depression prior to onset of a major depressive episode was significantly associated with a decreased probability of recovery from that episode; with each additional year, the likelihood of recovery was reduced by 7% (hazard ratio = 0.93; 95% CI, 0.89-0.98; P = .002).

Conclusions: Bipolar I major depression generally lasts longer than minor depression, and the duration of multiple episodes within an individual varies. However, the probability of recovery over time from an episode of major depression appears to decline with each successive episode.