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Oxidative stress is intrinsically linked to mental disorders, involving an imbalance between reactive species and antioxidant defenses, where catalase is an essential, ubiquitous antioxidant enzyme. The pleiotropic effects of antipsychotic drugs, used for schizophrenia and mood disorders, are not fully elucidated at the molecular level. This study characterized the binding of a highly effective but potentially dangerous antipsychotic, clozapine (CLZ), to commercial bovine liver catalase (BLC). Using various spectroscopic methods under simulated physiological conditions, we found a moderate binding affinity of CLZ for BLC (K_a = 1.4 × 10^-5 M^-1), subtly influencing the protein's secondary and tertiary structures and slightly increasing its thermal stability. CLZ efficiently protected BLC against free-radical-induced oxidation and preserved its catalytic activity for decomposing toxic hydrogen peroxide. The effect of CLZ on BLC antioxidant activity was dual: no significant effect at lower, physiologically relevant concentrations, but significant inhibition at saturating, toxic drug concentrations. Molecular docking and molecular dynamics results indicated the presence of two specific binding sites within BLC monomers, one located near its active site. In conclusion, our in vitro results indicate that CLZ's specific binding to BLC can be both beneficial and potentially harmful, and that this effect is dose-dependent.