52 phase and the magnitude of nocebo responses, but a meta-regression found no significant association (Q = 0.89, p = 0.35). Magnitude of nocebo responses based on the Risk of Bias score Lastly, we examined how RoB scores may be related to nocebo magnitudes. A meta-regression showed no significant relationship between RoB scores and the magnitude of nocebo responses for pain studies that used conditioning and verbal suggestions (Q = 0.75, p = 0.39), for pain studies that used only verbal suggestions (Q = 0.00, p = 0.95), for itch studies that used conditioning and verbal suggestions (Q = 0.08, p = 0.77), or for itch studies that used verbal suggestions alone (Q = 1.9, p = 0.05). Discussion We conducted a systematic review and meta-analysis of a total of 37 distinct nocebo studies on healthy participants. This meta-analysis showed that on average, nocebo effects were moderate to large in magnitude. The combination of verbal suggestions with classical conditioning yielded stronger nocebo responses on pain, but this may not necessarily be the case in the small number of itch studies. Measures of the type or intensity of pain or itch, and length of learning, did not explain the moderate heterogeneity in nocebo magnitudes between different studies. Timing of nocebo measurement in the first evocation trials yielded slightly larger nocebo magnitudes. Risk of bias was
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