Directionality of change in obsessive compulsive disorder and depression over six years of prospective follow-up

Major Depressive Disorder (MDD) is often comorbid with obsessive-compulsive disorder (OCD) yet little is known about the directionality of the association between OCD and depression symptoms. We aim to investigate the effect OCD symptoms has on depression symptoms and vice versa over an extended period of time. This is one of the first longitudinal studies to evaluate the relationship between OCD and depression in a large clinical sample. Participants (n = 324) were treatment-seeking adults with a primary diagnosis of OCD. OCD and depression symptoms were assessed annually over the six-year follow-up period. Random intercepts cross-lagged panel models (RI-CLPM) were conducted to compare unidirectional and bidirectional models over time. The best-fitting and most parsimonious model included paths with OCD symptoms predicting depression symptoms, but not vice versa. OCD symptom severity in a given year predicted next year depression severity. However, depression severity did not predict next-year OCD symptom severity in this sample. Our results suggest that depression severity may be secondary to OCD symptoms and treating OCD should be prioritized over treating depression.