This investigation is the studies on the solubility analysis for several pharmaceuticals. The equilibrium reactions leading to complex formation of Caffeine and Nicotinamide with Lidocaine and Saccharin have been studied. The equilibrium constant of each complexes have also been calculated. It is shown that complex formation may lead to an increase in the solubilities of the reactants, and that Nicotinamide has more complexing activity than Caffeine. The influence of chemical structure of each components on interaction is also discussed.