This study explores the utilization of expired pharmaceutical drugs, specifically Progynova 2 mg (estradiol valerate), as a sustainable solution for corrosion inhibition in mild steel exposed to a 1 M HCl medium at 30°C. Through a comprehensive analysis employing FTIR, mass loss, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), quantum chemical analysis (DFT), and scanning electron microscope (SEM), the research confirms the remarkable effectiveness of estradiol valerate (EPROG) in inhibiting mild steel corrosion, achieving an impressive 94.27% inhibition efficiency at a concentration of 600 ppm. Potentiodynamic polarization reveals mixed-type inhibition behavior, while EIS measurements indicate increased charge transfer resistance (Rct) and reduced double layer capacity (Cdl) with higher estradiol valerate concentrations, in line with Langmuir adsorption isotherm results. The DFT analysis of the EPROG inhibitor indicates that it use a donor-acceptor mechanism to interact with the metal surface. SEM analysis further substantiates the presence of a stable EPROG inhibitor layer on the mild steel surface, underscoring its corrosion inhibition properties and advocating for the sustainable repurposing of expired pharmaceuticals in environmental and structural preservation efforts.