<p>This study investigates the interactive effects of hydrogen and defects (vacancies and self-interstitial atoms—SIAs) on the structural and mechanical properties of zirconium using molecular dynamics simulations. Our findings reveal significant and complex interplay between these factors. The introduction of hydrogen leads to lattice expansion and a reduction in bulk and Young's moduli, while slightly increasing the shear modulus, indicating a weakening of stiffness. Vacancy defects further decrease mechanical moduli, while SIA defects exhibit a complex influence on elastic constants. Notably, the interaction between hydrogen and these defects exacerbates reductions in mechanical properties, pointing to a synergistic effect that compromises structural integrity. Ductility decreases with increasing hydrogen concentration, suggesting a trend toward brittleness, whereas hardness increases with hydrogen but decreases with vacancies and SIAs. These findings underscore the critical role of hydrogen and defects in altering zirconium's mechanical behavior, highlighting the importance of understanding these interactions for applications in different industries.</p>