The micellization of amphiphilic drug amitriptyline hydrochloride (AMT, an antidepressant) and conventional as well as gemini surfactants has been studied conductometrically in pure and mixed states in aqueous solutions at different temperatures to derive various physicochemical properties such as critical micelle concentration (cmc), ideal cmc (cmc(id)), counterion dissociation (g), standard Gibbs free energy (Delta G(m)(0)), enthalpy (Delta H-m(0)), and entropy of micellization (Delta S-m(0)), micellar mole fractions of surfactant (X-1, X-1(m)), mole fraction of surfactant in ideal state (X-1(id)), interaction parameter (beta), activity coefficients (f(1), f(2)), and excess free energy of mixing (Delta G(ex)). All the results indicate synergism and attractive interactions in the mixed systems.