The search for eco-friendly corrosion inhibitors for mild steel has driven interest in the valorization of expired pharmaceutical products as green alternatives to conventional toxic inhibitors. The present study investigated the synergistic inhibition behaviour of expired ciprofloxacin and iodide ions for mild steel in synthetic acid rain solution using gravimetric, surface morphology analysis and molecular dynamic simulation approaches. The results showed that the corrosion inhibition performance significantly improved in ciprofloxacin-iodide system and the inhibition performance reach approximately 97 % at low concentration. The surface morphology analysis showed that the inhibitor molecules are adsorbed on the mild steel surface, thereby decreasing the corrosion rate. The adsorption process follows the Frumkin adsorption isotherm. The experimental results correlated with the molecular dynamics simulation results. The findings in this research provide a practical strategy for the potential reuse of expired ciprofloxacin waste and the development of novel corrosion inhibitors.