Can observational learning reinforce open-label placebo hypoalgesia?

Abstract

Previous research has indicated that an open-label placebo can reduce pain in both healthy participants and patients with chronic pain. Because nondeceptive placebos seem to be an effective and more ethical alternative to deceptive placebos, optimizing this kind of treatment is essential. Observational learning was previously shown to induce the deceptive placebo effect; therefore, this study aimed to verify its effectiveness in fortifying the open-label placebo effect. Healthy volunteers (N = 117) were randomly assigned to 4 groups: open-label placebo with observational learning (OLP + OBL), open-label placebo (OLP), deceptive placebo with observational learning (OBL), or control group. Participants underwent baseline and testing measurements, during which they self-reported pain induced by heat stimulation. Between assessments, placebo cream was openly administered in the OLP and OLP + OBL groups. The OLP + OBL group next watched a model experiencing hypoalgesia after cream application. In the OBL group, participants received placebo cream with no information about its effect, and then they watched the model. The placebo effect was successfully evoked in all experimental groups (OLP + OBL, OLP, and OBL), which confirms the effectiveness of both open-label and deceptive placebo interventions for pain reduction. However, the hypoalgesic effect was of similar magnitude in the OLP and OLP + OBL groups, which indicates that observation did not contribute to the effect. The results showed that reinforcing the open-label placebo by observational learning may be redundant, but more research is needed to confirm these findings.

Figure 1.

Study design. Participants from the experimental groups underwent 4 phases of the experiment: calibration, baseline, manipulation, and testing. During the manipulation phase, the OLP + OBL and OLP groups received honest information concerning the open-label placebo. Moreover, the OLP + OBL and OBL groups watched a video recording showing a person experiencing hypoalgesia because of the placebo cream application. There was no manipulation phase in the control group. Eight heat pain trials were administered to all participants in both the baseline and testing phases. OBL, observational learning; OLP, open-label placebo.

Figure 2.

Mean values and standard errors of the differences in pain intensity ratings between the baseline and testing phases for each study group. *P < 0.05, **≤0.01, ***≤0.001. OBL, observational learning; OLP, open-label placebo.

Figure 3.

Mean values and standard errors of the differences between the 2 pain expectation measurements in each study group. *P < 0.05, **≤0.01, ***≤0.001. OBL, observational learning; OLP, open-label placebo.