Peripheral CCK and ß-Endorphin as Potential Neuroendocrine Markers of Nocebo Effects: Evidence from a Multiple-Threat Pain Paradigm.

INTRODUCTION: Nocebo effects are shaped by negative treatment-related expectations and experiences and can contribute to adverse treatment outcomes. They have been linked to neuroendocrine alterations, yet reliable peripheral biomarkers remain elusive. Although cholecystokinin (CCK) has long been implicated in nocebo hyperalgesia, direct evidence in humans remains limited. β-Endorphin (β-END) is another promising candidate given its established role in endogenous pain modulation and placebo analgesia. The present study aimed to investigate whether peripheral CCK and β-END responses are associated with nocebo effects in the visceral pain modality.

METHODS: In this biomarker-focused analysis of the experimental NOVIS trial, healthy volunteers (N = 100) underwent a multiple-threat pain paradigm comprising visceral (rectal distension) and somatic (cutaneous heat) pain stimulation. Participants were randomized to receive negative versus neutral verbal treatment suggestions and either an adverse or a neutral treatment experience. Plasma concentrations of CCK and β-END were assessed during the treatment phase (T1), after the treatment phase (T2), and following the subsequent test phase (T3). Visceral pain unpleasantness ratings served as the primary behavioral measure of nocebo responding. Generalized linear mixed models were used to examine between-group differences in neuroendocrine responses, responder versus non-responder differences based on nocebo-induced changes in visceral pain unpleasantness, and exploratory sex differences.

RESULTS: For CCK, between-group analyses yielded no significant differences. The post-hoc responder analysis revealed that nocebo responders exhibited significantly higher peripheral CCK concentrations during treatment (T1) compared to non-responders, with no differences at subsequent time points. Women exhibited significantly higher β-END concentrations than men across all groups and time points, with no nocebo-related group differences or changes observed.

CONCLUSION: Elevated CCK concentrations during treatment may constitute a dispositional marker of nocebo susceptibility or an early anticipatory neuroendocrine response to treatment-related interpersonal cues. Higher β-END in women may reflect sex-related variation in peripheral opioid-associated neuroendocrine responses rather than a nocebo-specific mechanism. These findings may inform future efforts to identify biological and contextual factors that shape nocebo susceptibility and, ultimately, to develop more individualized communication strategies in clinically vulnerable populations such as persons living with chronic visceral pain in disorders of gut-brain interactions.