The inhibitive action of lansoprazole (LPZ) on stainless steel 304 corrosion and permeation of hydrogen gas in 2N H3PO4 has been analyzed using weight loss, gasometric and electrochemical studies. The antibiotic seems to be more effective in reducing the dissolution of steel in 2N H3PO4. Potential-Current curves clearly indicated that the compound observes mixed mode of inhibition in 2N H3PO4. Hydrogen permeation and EIS measurements have confirmed that LPZ retards the corrosion of SS 304 effectively. The quantum mechanical studies validated the performance of the inhibitor molecule through its effective adsorption on steel surfaces using theoretical values of EHOMO, ELUMO, ΔE and dipole moment of inhibitor.