Effect of defense mechanisms on the longitudinal development of interpersonal problems during outpatient therapy

This longitudinal observational study investigates the relationship between patients’ defense mechanisms before outpatient therapy and their interpersonal problems during early treatment, exploring how specific defense mechanisms are associated with interpersonal problems, a clinically relevant factor for therapy planning. Participants (N=286) from a German outpatient sample completed baseline assessments prior to their first therapy session, including self-report measures of defense styles (Defense Style Questionnaire DSQ), emotion regulation (Difficulties in Emotion Regulation Scale - Short Form DERS-SF), structural integration (Operationalized Psychodynamic Diagnosis - Structure Questionnaire Short Version OPD-SQS), and interpersonal problems (Inventory of Interpersonal Problems IIP-32). Follow-up assessments were conducted at approximately 6 and 12 months. Linear mixed models were used to examine longitudinal changes in interpersonal problems and their association with baseline defense styles and defense mechanisms, adjusting for age, sex, therapy duration, structural integration, and emotion regulation difficulties. Particularly, the intermediate (neurotic) defense style was associated with higher levels of interpersonal problems across timepoints. However, defense styles did not significantly predict changes in interpersonal problems over time. In contrast, a more nuanced analysis at the level of defense mechanisms revealed that projection, undoing, and reaction formation were associated with greater interpersonal difficulties, while anticipation was associated with fewer difficulties. Projection showed a robust interaction with time, indicating its relevance for predicting individual change trajectories. These findings suggest that individual defense mechanisms provide added predictive value over aggregated defense styles when assessing interpersonal functioning in early outpatient therapy. From a clinical perspective, the differentiated assessment of specific defenses may improve treatment planning in psychodynamic therapy, although further research is warranted.