It has previously been found that the undesirable side effects of enhancers may be reduced, virtually without affecting their promoting absorption actions, when they are used in combination with a cyclodextrin. Many enhancers are amphiphilic moieties able to form micelles in solution. The enhancing effect is ascribed to the free molecules in solution. Their toxic effects seem to be linked to the solubilization of cell membrane components (Such as phospholipids or cholesterol), due to micelles formed by the enhancers. A study on the influences of cyclodextrins on critical micellar concentration (cmc) shifting has been carried out by surface tension measurements. The formation of a complex in solution between the cyclodextrin and the enhancer shifts cmc to higher values, and changes the ratio between free and micellized molecules of the enhancer, thus minimizing its toxic effects. Laureth-9, quaternary ammonium salts and cholic acid derivatives were considered as enhancers. Changes in buffering salts and tonicity of the measuring medium were also taken into consideration as formulative variables.