The European Agreement on Work-Related Stress defines stress as a state characterized by physical, psychological, or social complaints or dysfunctions resulting from individuals feeling unable to meet the demands or expectations placed upon them (Broughton, 2004). This definition underscores the global recognition of health-related problems associated with stress (Fisch et al., 2020a; Gnall et al., 2023; Mazure et al., 2023; Popescu et al., 2023; Sara et al., 2023; Walther and Wirtz, 2023). In Germany, a survey of 1,200 adults found that 61% reported experiencing stress either frequently or occasionally (Wohlers and Hombrecher, 2016).

Hypnosis is a state of focused attention and heightened suggestibility that can be induced by a trained professional. It has been used as a therapeutic tool for a variety of clinical purposes, including stress reduction. A 2017 systematic review examined the effects of hypnosis in patients with perceived stress. While six of the nine included studies reported significant positive effects of hypnosis on stress reduction, all of the included studies had a high risk of bias and used exploratory designs (Fisch et al., 2017). Since the publication of the aforementioned review, our research group has conducted a multicenter randomized controlled trial offering group hypnosis for stress reduction and improved stress coping, which showed a reduction in perceived stress in the hypnosis group compared to the control group at both 5 and 12 weeks (Fisch et al., 2020a). Other studies have also shown that hypnosis leads to a lower perception of stress (Payrau et al., 2017; Olendzki et al., 2020; Slonena and Elkins, 2021; Vahdat et al., 2022).

Although scientific evidence from other fields suggests that expectations are able to positively influence treatment outcomes for a range of medical conditions and procedures (Mondloch et al., 2001; Constantino et al., 2011; Auer et al., 2016), little research has examined whether expectations to hypnosis might be able to predict treatment outcomes.

Patients’ expectations may encompass their beliefs about the efficacy of hypnosis and their anticipated outcomes from the treatment in question. To date, few studies have attempted to discern whether individuals with high expectations of positive outcomes to hypnosis will experience more significant benefits compared to those with low expectations (Sliwinski and Elkins, 2017; De Pascalis et al., 2021; Egli et al., 2022). This debate is imperative because it raises questions about the role of psychological factors in the therapeutic process and the validity of hypnosis as a treatment modality in its own right. A perspective that has not been very well researched suggests that patients with different expectations to hypnosis may experience a different therapeutic effect, whereby their belief in the efficacy of the treatment may influence their response to it (Frisaldi et al., 2015; Koban et al., 2017). In this respect, participants’ expectations may confound the interpretation of study results, making it challenging to isolate the specific effects of hypnosis itself. As indicated by other studies, expectations also contribute to placebo and nocebo effects (Petrovic et al., 2005; Wager et al., 2007; Tracey, 2010). Consequently, they could also influence the effectiveness of hypnotic interventions (Kirsch, 1985). Moreover, it is assumed that hypnosis in clinical practice can induce altered states of consciousness independently of initial expectations and produce therapeutic benefits through suggestion and relaxation techniques.

We performed a secondary data analysis to examine whether treatment expectations to a group hypnosis program for stress reduction and improved stress coping would be able to predict perceived stress in the previous week, as measured on a visual analog scale, after 5 weeks.

Detailed sociodemographic characteristics of the sample are outlined in the original study article (Fisch et al., 2020a). Table 1 shows the comparison of sociodemographic characteristics between those with high and low expectations to hypnosis in the intervention group. We observed no relevant differences at baseline in individuals with high and low expectations.

Unadjusted linear regressions showed that expectations to hypnosis were not associated with a change in perceived stress between baseline and after 5 weeks (B = 0.326, t = 0.239, p = 0.812, R² = 0.001) (Figure 1).

Similarly, adjusted linear regressions showed that expectations to hypnosis were not associated with a change in perceived stress between baseline and after 5 weeks (B = 0.639, t = 0.470, p = 0.641, R² = 0.168) (Figure 2).

Contrary to previous research that has shown that expectations predict treatment outcomes (e.g., Auer et al., 2016), our findings showed no association between participants’ expectations and perceived stress after 5 weeks. Consequently, other contextual factors, such as hypnotic relaxation, active resource activation, and reframing techniques and group interactions may have played a greater role than expectations in determining treatment outcomes.

Our results showed that overall participants had relatively high expectations at baseline (M = 13.74, SD = 2.72) before being randomized to and participating in the group hypnosis program. Therefore, it could be suggested that future studies should include individuals with more diverse expectations in order to determine how these may be associated with varying treatment outcomes. For example, research on recovery expectations in patients with back pain (Kamper et al., 2015) has shown that the level of expectations may indeed predict treatment outcomes, with high expectations leading to the greatest improvement compared to moderate and low expectations. Further to this, participants’ baseline level of stress was relatively high in our study. However, future research which includes individuals with low, moderate, and severe levels of stress is necessary to determine the interplay between a diverse range of expectations and the outcome under investigation.

Information on patients’ expectations was only collected at baseline. As a result, we do not know whether expectations changed over the course of the group program. Yet, it has been proposed that patient expectations to treatment should be assessed before, during and after treatment as expectations may change over the course of treatment (Kamper et al., 2015; Laferton et al., 2017).

In addition, we did not assess whether trial participants had previously undergone hypnosis. Nevertheless, it may be important to ascertain this, as expectations may be influenced by previous exposure to hypnosis. For example, research has shown that individuals who had previously received acupuncture prior to participating in a trial investigating different briefing contents before a minimal acupuncture treatment in patients with chronic low back pain had higher expectations than those who had never received acupuncture. However, the study authors caution that higher expectations cannot be explained solely by patients’ previous experience with acupuncture, but that the relative contribution of contextual factors on patients’ pre-treatment expectations should also be considered (Zieger et al., 2022).

Although the ETS has shown to be a valid and reliable scale for measuring outcome expectations, it was originally developed in the context of acupuncture (Barth et al., 2019). While the scale has been used to determine outcome expectations across a variety of studies, there has been mixed evidence as to whether expectations predict therapeutic outcomes (de Matos et al., 2020; Barth et al., 2021; Egli et al., 2022; Zieger et al., 2022; Müller-Schrader et al., 2023). Further research should therefore be conducted using different treatment outcomes and patient populations to further explore to what extent the original scale and any modified versions are indeed able to accurately predict outcome expectations. Furthermore, the scale is not based on any theoretical models and only examines positive outcome expectations. Nonetheless, this may be problematic, as the absence of theory and negative outcome expectations could lead to important constructs being missed, thus limiting researchers’ ability to determine whether expectations do indeed predict treatment outcomes.

Lastly, we did not explore the potential influence of other variables, such as trust in the therapist. These factors may interact with expectations in complex ways that were not addressed in our research.

To our knowledge this is the first study that has explored the predictive value of expectations on hypnosis for stress reduction. It contributes to the growing understanding of the relationship between patient expectations and treatment outcomes in general, but more specifically in the field of hypnotherapy. In addition, it is based on a randomized controlled multicenter trial with high adherence rates and whose intervention was thoroughly designed and delivered by qualified hypnotherapists (physicians or psychological psychotherapists). We also recognize that the small number of study participants is a clear limitation of this secondary analysis, which may affect the generalizability of our findings. Furthermore, we did not originally plan to perform any further analysis, and therefore the results can only be interpreted in an exploratory manner.

In this analysis, we found no association between participants’ expectations and perceived stress at 5 weeks in the intervention group. Our results suggest that factors contributing to the effect of hypnotherapy may have acted independently of participants’ expectations. Further research is required to explore the complex relationship between pre-therapy expectations and hypnotherapy outcomes.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The studies involving humans were approved by Ethical Approval No. EA1/067/18; Ethics Committee of the Charité – Universitätsmedizin Berlin; Charité Mitte, Charitéplatz 1 (local address: Virchowweg 10) 10117 Berlin. The studies were conducted in accordance with the local legislation and institutional requirements. The participants provided their written informed consent to participate in this study.

JS: Writing – original draft, Writing – review & editing. MT: Conceptualization, Funding acquisition, Investigation, Project administration, Supervision, Writing – review & editing. BB: Conceptualization, Project administration, Supervision, Writing – review & editing. SF: Conceptualization, Funding acquisition, Investigation, Writing – review & editing. SK: Methodology, Software, Writing – original draft, Writing – review & editing.