The inhibitive effect of expired Cidamex drug on aluminum in 1M HCl solution was studied using weight loss, hydrogen evolution, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) and electrochemical frequency modulation (EFM) techniques. The results indicate that Cidamex is good inhibitor and inhibition efficiency improved with concentration and reached 99.6% at 300 ppm. Thermodynamic activation parameters that govern the process were deduced from the temperature dependence. Potentiodynamic polarization curves indicated that this drug behaves as mixed-type inhibitor. This drug was adsorbed on aluminium surface follows Langmuir adsorption isotherm. The results obtained from all investigated techniques are in good agreement.