Pyruvate kinase (PK) deficiency is a rare, hereditary disease characterized by chronic hemolytic anemia. Iron overload is a common complication regardless of age, genotype, or transfusion history. Mitapivat, an oral, allosteric PK activator, improves anemia and hemolysis in adult patients with PK deficiency. Mitapivat's impact on iron overload and ineffective erythropoiesis was evaluated in adults with PK deficiency who were not regularly transfused in the phase 3 ACTIVATE trial and long-term extension (LTE) (NCT03548220/NCT03853798). Patients in the LTE received mitapivat throughout ACTIVATE/LTE (baseline to Week [W] 96; mitapivat-to-mitapivat [M/M] arm) or switched from placebo (baseline to W24) to mitapivat (W24 to 96; placebo-to-mitapivat [P/M] arm). Changes from baseline in markers of iron overload and erythropoiesis were assessed to W96. Improvements in hepcidin (mean [95% confidence interval ⟨CI ⟩] 4770.0 ng/L [-1532.3, 11,072.3], erythroferrone (-9834.9 ng/L [-14,328.4, -5341.3]), soluble transferrin receptor (-56.0 nmol/L [-84.8, -27.2]), and erythropoietin (-32.85 IU/L [-54.65, -11.06]) were observed in the M/M arm (n=40) from baseline to W24, sustained to W96. No improvements were observed in the P/M arm (n=40) to W24; however, upon transitioning to mitapivat, improvements similar to the M/M arm were seen. Mean (95% CI) changes from baseline in liver iron concentration (LIC) by magnetic resonance imaging (MRI) at W96 were -2.0 mg Fe/g dry weight (dw) (-4.8, -0.8; M/M arm) and -1.8 mg Fe/g dw (-4.4, 0.80; P/M arm). Mitapivat is the first disease-modifying pharmacotherapy shown to have beneficial effects on iron overload and ineffective erythropoiesis in patients with PK deficiency.