(PS7-12) Examining Homework Adherence Across OCD Domains and EX/RP: Does It Explain Differences in Treatment Outcome?

Exposure and response prevention (EX/RP) is a first-line treatment for Obsessive Compulsive Disorder (OCD); however, up to a third of patients do not achieve optimal symptom remission after a standard course of treatment. Prior research suggests that OCD symptom domains influence EX/RP outcomes, with contamination and responsibility for harm domains responding more effectively and more quickly than unacceptable thoughts and “other” domains. Patient adherence to exposure homework is a well-established predictor of favorable EX/RP outcomes and has been shown to mediate the relationship between some predictor variables and treatment responses (Simpson et al., 2011). This study examines whether homework adherence differs across OCD domains, how it relates to EX/RP outcomes, and whether it mediates the relationship between OCD domains and treatment response. Based on prior findings, we hypothesize that homework adherence mediates the relationship between OCD domain types and EX/RP outcomes.

A total of 137 adults with OCD received 17 sessions of EX/RP over 8 weeks as part of a randomized controlled trial. Independent raters categorized five OCD domain groups: contamination, responsibility for harm, unacceptable thoughts, symmetry, and an “other” category for symptoms not fitting within the established domains. We examined group differences in 1) homework adherence, as measured by the Patient EX/RP Adherence Scale (PEAS; Simpson et al., 2010), and 2) EX/RP outcomes, as measured by post-treatment scores on the Yale-Brown Obsessive Compulsive Scale (Y-BOCS, Goodman et al., 1989) severity scale.

Multiple linear regression analyses assessed the relationships between PEAS scores, OCD domain, and Y-BOCS severity scores. Higher average PEAS scores were significantly associated with greater symptom reduction over the 8-week treatment period (PEAS x Time interaction: b=-.56, 95% CI [-.75, -.38}, t(129)=-6.08, p< .001) and lower post-treatment Y-BOCS scores (b=-5.46, 95% CI: [-6.66, -4.26], t(119)=9.03, p< .001). However, when controlling for homework adherence, significant differences in Y-BOCS symptom severity across OCD domains (see Tyler et al., 2025) remained significant (Responsibility vs. Unacceptable Thoughts p=.004 and Responsibility vs. Other p< .001). No significant differences between average PEAS scores were found between groups (p=.097), with scores ranging from M=4.9-5.44 (SD=.53-.65).

Findings indicate that while homework adherence is a strong predictor of EX/RP treatment outcomes, it does not fully explain the differences in treatment response across OCD domains. Patients in the contamination and responsibility for harm categories demonstrated better treatment responses, but their homework adherence rates did not differ significantly from those in the unacceptable thoughts and “other” domains. This suggests that factors beyond homework adherence, such as domain-specific treatment barriers (e.g., differences in violations of fear expectations), may contribute to the differential EX/RP outcomes. The results highlight the need for personalized interventions that consider both adherence and the unique characteristics of OCD symptom domains to optimize treatment efficacy.