Baseline corticosteroids exposure is associated with inferior clinical outcomes in patients with non-small-cell lung cancer (NSCLC) treated with programmed cell death-1 (PD-1) axis blockade. Dexamethasone is a potent corticosteroid used in the prevention of chemotherapy-associated adverse events (CAAEs).Since dexamethasone has immunosuppressive properties, this study attempted to elucidate its effects on the efficacy of immunotherapy plus chemotherapy in patients with non-squamous NSCLC.The study retrospectively analyzed the medical records of 254 advanced non-squamous NSCLC patients who received front-line treatment with a PD-1 pathway inhibitor and platinum-based chemotherapy at three academic institutions. The average dosage of prophylactic dexamethasone per chemotherapy cycle was calculated. Patients were divided into three groups based on the dose of dexamethasone: High-d (≥24 mg), Moderate-d (12-24 mg), and Low-d (<12 mg). Spearman's rank correlation was used to assess the correlation between the dosage of dexamethasone and progression-free survival (PFS). Logistic regression was used to assess the correlation between dexamethasone dosage and the occurrence of immune related adverse effects (irAE). Univariate and multivariate Cox proportional hazards regression models were used to analyze the differences in survival among the different dexamethasone dosage groups.The dosage of prophylactic dexamethasone was not significantly correlated with PFS (Spearman's rho = -0.103, P = 0.098). Results from the univariate [hazard ratio (HR)Low-d/High-d, 1.00; P = 0.997; HRModerate-d/High-d, 0.85; P = 0.438] and multivariate (HRLow-d/High-d, 0.71; P = 0.174; HRModerate-d/High-d, 0.87; P = 0.512) analyses showed no significant association between dexamethasone and PFS. Dexamethasone did not have significant effect on the objective response rate, disease control rate or overall survival. The toxicity profiles of irAE were similar across all three groups.The results of this study suggest that the use of prophylactic dexamethasone does not have an adverse effect on the clinical outcomes of non-squamous NSCLC patients treated with PD-1 blockade therapy and chemotherapy. Routine use of dexamethasone for preventing CAAEs should be recommended for patients undergoing combined immunotherapy and chemotherapy.Copyright © 2023 The Author(s). Published by Elsevier B.V. All rights reserved.