BACKGROUND: Levodopa-induced dyskinesia (LID) is a complication of Parkinson's disease (PD) treatment. While the placebo effect is a known component in PD clinical trials, its specific magnitude in the context of LID is not well characterized. OBJECTIVE: To quantify the magnitude of the placebo response in LID trials and to identify potential moderators of this effect. METHODS: We conducted a systematic review and meta-analysis of double-blind, placebo-controlled trials in patients with PD and LID. The primary outcome was the change in dyskinesia severity in the placebo arm, pooled using random-effects model. RESULTS: Thirty one publications, comprising 1329 patients, were included. Data were stratified by reporting methodology: 16 studies provided primary LS mean change data, 11 provided simple change and the remaining studies contributing solely to subgroup analyses. The primary meta-analysis, revealed a statistically significant placebo response of moderate magnitude (pooled SMD = -0.48, p < 0.0001), with significant heterogeneity (I2 = 47.6%). Subgroup analyses showed this corresponded to clinically measurable improvements, including a mean reduction of -6.78 points on the UDysRS and an increase of +1.27 h in "Good On Time." Meta-regression identified that a larger placebo effect was significantly associated with older patient age (p = 0.014), a higher proportion of female participants (p = 0.016), and shorter study duration (p = 0.006). CONCLUSION: The placebo response in LID is a consistent, clinically relevant phenomenon modulated by patient demographics and trial duration. Quantifying this response is essential for design and accurate interpretation of future trials.