In this study, the surface properties (in water and in the presence of varying concentrations of NaCl, CTAB, and TX-100) of four amphiphilic drugs are presented. The parameters evaluated are cmc (critical micelle concentration), Gamma(max) (maximum surface excess concentration at the air/water interface), and A(min) (minimum area per surfactant molecule at the air/water interface). Gamma(max) increases and cmc/A(min) decreases with increasing concentration of the additives. The cmc values calculated using a dye solubilization method for the systems also follow the same trend. The behavior is explained on the basis of counterion adsorption and mixed micelle formation.