Open- and closed-label placebo and nocebo suggestions about a sham transdermal patch.

Objective Placebo effects may occur when it is known that an inert substance is given (i.e., open-label placebo). It is not yet clear whether these effects are similar to concealed (i.e. closed-label) placebo effects for itch, or whether nocebo effects can be induced under open-label conditions. Methods Healthy volunteers (n=112) were randomized to an open-label (I) or closed-label (II) positive suggestions group, or an open-label (III) or closed-label (IV) negative suggestions group. Participants were told, as cover story, that a transdermal caffeine patch would be applied that positively influences cognitive abilities and, as a side effect, positively or negatively (depending on group allocation) influences itch. Participants in the open-label groups were given a rationale explaining placebo and nocebo effect mechanisms. Itch (the primary outcome) was induced at baseline and post-suggestions by histamine iontophoresis. Results Analyses of variance revealed significantly lower itch in the positive compared to the negative suggestions groups for both open- and closed-label contexts (all p≤.008, Cohen's d≥0.47). Self-rated skin response was less severe following positive versus negative suggestions (all p≤.017, Cohen's d≥0.33), but no effects on physical skin response were found (all p≥.23, Cohen's d≤0.30). Conclusion Itch can be reduced by positive compared to negative suggestions under both open- and closed-label conditions. These findings indicate that open-label suggestions may potentially be a tool to utilize placebo effects for self-reported outcomes in clinical practice, for example by explaining the role of expectancy in treatment. It needs to be investigated further under which circumstances an open-label rationale may impact placebo and nocebo effects.