UV spectroscopy shows that dextromethorphan, guaifenesin and caffeine bind to ferrous gluconate, causing their spectra to shift. From this change, it is calculated that the binding energy is in the order of caffeine > guaifenesin ≈ dextromethorphan. This is consisternt with the electrochemical/potentiometric data obtained in a previous study which detected electrons emitted from these drug-iron complexes if they were irradiated by UV light or connected to solutions having different electrochemical potentials. Based on the result of this study, ferrous gluconate is more useful for the rapid screening of the drug-heme or drug-iron interactions in biological/pharmacological systems than free (unbound) iron. It may also find utility in energy production, bio-sensing and photo-electronics.