Prospective study of substance-induced and independent major depressive disorder among individuals with substance use disorders in a nationally representative sample.

BACKGROUND

Depression and substance use disorders (SUDs) commonly co-occur, which presents diagnostic challenges in classifying independent major depressive disorder (MDD) versus substance-induced depressive disorder (SIDD). It remains unclear if distinct characteristics and/or patterns in temporal course distinguish MDD-SUD and SIDD to guide these decisions. Further, evidence suggests that a significant portion of individuals with SIDD are later reclassified as having independent MDD. Continued research to improve our understanding of differences between these two and changes in reclassification over time is necessary for diagnostic clarification and to guide clinical decisions when treating depression in the context of SUDs.

METHODS

The current study compared individuals with MDD-SUD versus SIDD at baseline and examined reclassification of DSM-IV Axis I diagnoses over a 3-year follow up in a large, nationally representative epidemiological sample (n = 2,121).

RESULTS

Findings demonstrated that SIDD was extremely rare at both time points. At baseline, individuals with SIDD were more likely to be non-White, have less education, less likely to have insurance, less likely to have dysthymia or alcohol abuse, and more likely to have drug dependence compared to those with independent MDD. Of individuals with SIDD at Wave 1 who had a depressive episode between Waves 1 and 2, the overwhelming majority (>95%) had an independent MDD, not SIDD, episode. There were no significant group differences in the incidence of other mood disorders or SUDs at Wave 2.

CONCLUSIONS

Findings have important etiological and treatment implications for the classification and treatment of depression in the context of SUDs.