Reliably identifying good placebo responders has pronounced implications for basic research on, and clinical applications of, the placebo response. Multiple studies point to direct verbal suggestibility as a potentially valuable predictor of individual differences in placebo responsiveness, but previous research has produced conflicting results on this association.
In two double-blind studies, we examined whether behavioural direct verbal suggestibility measures involving a correction for compliance would be associated with individual differences in responsiveness to conditioned and unconditioned placebo hypoalgesia using an established placebo analgesia paradigm. In Study 1 (N = 57; MAge = 23.7, SD = 8.1; 77% women), we used behavioural hypnotic suggestibility as a predictor of placebo hypoalgesia induced through conditioning and verbal suggestion whereas in Study 2 (N = 78; MAge = 26.1, SD = 7.4; 65% women), we measured non-hypnotic suggestibility and placebo hypoalgesia induced through verbal suggestion without conditioning.
In Study 1, the placebo hypoalgesia procedure yielded a moderate placebo response (g = 0.63 [95% CI: 0.32, 0.97]), but the response magnitude did not significantly correlate with hypnotic suggestibility (rs = .11 [-.17, .37]). In Study 2, the placebo procedure did not yield a significant placebo response across the full sample (g = 0.11 [-0.11, 0.33]), but the magnitude of individual placebo responsiveness significantly correlated with non-hypnotic suggestibility (rs = .27 [.03, .48]).
These results suggest that the extent to which direct verbal suggestibility captures variability in placebo responsiveness depends on the use of conditioning and highlights the utility of suggestibility as a potential contributing factor to placebo responding when placebo hypoalgesia is induced through verbal suggestions.