How many well vs. unwell days can you expect over 10 years, once you become depressed?

Prognostic studies of major depression have mainly focused on episode remission and relapse, and only a limited number of studies have examined long-term course of depressive symptomatology at threshold and subthreshold levels.

The Group for Longitudinal Affective Disorders Study has conducted prospective serial assessments of a cohort of heretofore untreated major depressive episodes for 10 years under naturalistic conditions.

Of the 94 patients in the cohort, the follow-up rate was 70% of the 11,280 person-months. Around 77% of the follow-up months were spent in euthymia, 16% in subthreshold depression and 7% in major depression. Duration of the index episode before reaching recovery was the only significant predictor of the ensuing well time.

On average, patients with major depression starting treatment today may expect to spend three quarters of the next decade in euthymia but the remaining one quarter in subthreshold or threshold depression.