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Background: Wide fluctuations in placebo responses have been reported in phase 3 trials of systemic therapies for moderate-to-severe plaque psoriasis. Methods: In this systematic review and meta-analysis, we assessed placebo responses in phase 3 trials of systemic therapies for moderate-to-severe plaque psoriasis. The medical databases PubMed Medline, Embase, and Web of Science were searched for studies reporting on phase 3 psoriasis trials. A proportion meta-analysis determined the proportion of placebo-treated psoriasis patients obtaining a 75, 90, or 100% reduction in Psoriasis Area and Severity Index (PASI), that is, PASI75, PASI90, or PASI100, respectively, at week 12. In the assessment of PASI75 response, 44 trials with a total number of 7,972 patients were included. Conclusion: In pooled analyses, 5.2% (95% CI 4.7–5.7%) obtained PASI75, 2.1% (95% CI 1.7–2.4%) obtained PASI90, and 0.3% (95% CI 0.1–0.5%) obtained PASI100 among placebo receivers. No temporal changes were observed. The overall proportion of placebo responders in phase 3 psoriasis trials is low and does not appear to be increasing in recent years.

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