In the current study, outdated Ampicillin drug (AMP) was assessed as a potent and environmentally friendly corrosion inhibitor for 60Cu-40Zn brass by gravimetric analysis, in nitric acid solution in a concentration range of 0.5M-2M. The findings revealed that AMP exhibited high corrosion inhibition performance, and its efficiency increased with the increase of its concentration and the concentration of nitric acid. In addition, potentiodynamic polarization (PDP) curves, electrochemical impedance spectroscopy (EIS), and surface analysis were conducted in 0.5 M HNO₃ solution. Ampicillin was found to act as a mixed-type inhibitor, and its inhibitory efficiency increased with the addition of AMP up to 92% at its optimal concentration of 10 mM. However, it decreased slightly with increasing temperature. The adsorption thermodynamic parameters demonstrated that the medicine adsorbed onto a brass surface in accordance with the Langmuir isotherm, via physisorption and chemisorption mechanism. Scanning Electron Microscopy (SEM), Energy Dispersive X-ray (EDX) and   FT-IR/ATR analysis clearly evidenced the strong adsorption of AMP onto the brass surface, leading to higher corrosion resistance of the brass alloy in the inhibitive solution. Theoretical parameters of drug molecules were computed, using density functional theory (DFT) and Fukui indices, to better understand the adsorption mechanism of AMP molecules onto the brass surface. A close agreement between quantum calculations and experimental results was observed.