Objective: Emotion regulation and social processes that longitudinally predict depressive symptom change have not yet been investigated as mechanisms of change within a residential treatment context for homeless veterans with substance use issues. 

Methods: A longitudinal data analysis of 186 homeless veterans enrolled in a six-month residential rehabilitation and addiction treatment program was conducted to investigate the role of six different emotion regulation variables as well the impact of two relationship quality constructs when measured at three time points across treatment. 

Results: A large effect size reduction in depressive symptoms occurred during treatment (η2 = .233), and further analyses revealed that early treatment changes in a single subtype of emotion regulation, one's ability to tolerate distress while engaging in goal-directed behavior, was the only mechanism that preceded continued reductions in depressive symptoms later in treatment (β = .13, p < .001). Social mechanisms of change were not strong predictors of depressive symptom reduction. 

Conclusions: Distress tolerance skills, psychoeducation on the habituation process, and focusing on goal achievement may be particularly beneficial when treating substance use issues in homeless veterans who are also experiencing depressive symptoms during residential treatment.