(PS7-21) Patient Adherence Predicts and Mediates Outcome from Exposure and Response Prevention in Adults with Obsessive-Compulsive Disorder

Introduction: Exposure and response prevention therapy (EX/RP) is a well-supported, evidence-based treatment for OCD. Despite this, one-third of patients do not achieve minimal symptoms after EX/RP treatment delivered by expert providers. Research has examined factors that predict treatment outcomes, with patient adherence to EX/RP (particularly between-session homework) as one of the most robust predictors. Although patient adherence plays an integral role, limited research has explored the factors associated with patient adherence to EX/RP and its role as a mediator of treatment outcome.

Methods: Our sample consisted of 121 adults with OCD who received a course of EX/RP over 8 weeks as part of an NIMH-funded study (Simpson et al., 2021). Patient adherence was rated by the therapist at each exposure session using the Patient EX/RP Adherence Scale (PEAS; Simpson et al., 2010). We investigated factors previously identified as being associated with EX/RP outcome and/or patient adherence (pre-treatment OCD severity, avoidance, treatment expectancy, quality of life, OCPD traits, and years of education). Variables that significantly predicted patient adherence were then entered into a final model to examine the role of patient adherence as a mediator of EX/RP treatment outcome.

Results: Participants demonstrated on average “good” adherence to EX/RP, as measured by the PEAS. Regression analyses revealed that patient adherence significantly predicted post-treatment YBOCS severity scores. Treatment expectancy, avoidance, and years of education significantly predicted patient adherence. The mediation analyses found that patient adherence fully mediated the association between treatment expectancy and post-treatment YBOCS severity.

Discussion: Our results that patient adherence predicted EX/RP outcome and that treatment expectancy, pre-treatment avoidance, and years of education predict patient EX/RP adherence confirm and extend prior findings. Our result that patient adherence mediates the association between treatment expectancy and outcome is a novel finding in the field. Together, these data indicate that clinicians should focus on increasing treatment expectancy and decreasing avoidance at the very start of EX/RP. Future research should explore specific strategies for accomplishing both and testing their effects on patient adherence and EX/RP outcomes.