Inpatient’s, therapist’s and staff’s expectations regarding treatment and their effects on placebo response in the psychiatric ward – results from an add-on oxytocin RCT

Objectives: Patient’s and therapist’s expectations are considered an important factor influencing placebo response in experimental and therapeutic settings. Nevertheless, the placebo effects of common neurological facilitators that promote treatment efficacy have not been explored. In the present study we examined the estimations of patients, therapists, and staff members, regarding their treatment type and assessed their influence on the facilitating effects of oxytocin. Methods: Patients (N = 87) were randomized and double-blindly allocated to receive either oxytocin or placebo, twice daily for a period of four weeks, as part of a larger randomized, double-blind, placebo-controlled trial. Patient’s, therapist’s and staff’s expectations were assessed based on their estimation of treatment type (agent or placebo). Multilevel modeling and univariate and multivariate regression analysis were performed to assess the effects of patient’s, therapist’s, and staff’s estimations on treatment outcome beyond the effects of treatment type. Results: Staff’s, therapist’s, and patient’s estimations were significantly associated with treatment outcomes. Nevertheless, only therapist’s and patient’s estimations significantly predicted improvement beyond actual administration, with therapist’s and patient’s estimations associated with improvement in trait anxiety (STAI-T, B=-1.80, p <.05, and B=-2.02, p <.05, respectively); therapist’s estimations were associated with improvement in general distress (OQ-45, B=-3.71, p <.05), and patient’s estimations were associated with symptom relief (HSCL-11, B=-0.13, p <.05). Overall, patient’s estimations had a higher relative contribution to treatment success, with standardized coefficients across scales ranging from − 0.06 to -0.26. Conclusions: The neurobiological factors that promote treatment success are also influenced by patient’s and therapist’s expectations. Future studies should consider these effects when examining their impact in inpatient settings.