Abstract: AimTo study the drug release mechanism of famotidine time-controlled release pellets and to explore the mechanism of “organic acid-induced type drug delivery system”. MethodsThe effects of dissociated and undissociated forms of succinic acid on the drug release behavior of famotidine time-controlled release pellets were studied from the following aspects: ion-exchange reaction, hydration, ^etc. ResultsThe dissociated succinic acid created new ionic circumstances by ion-exchange reaction with Eudragit RS100. Whereas undissociated succinic acid increased the flexibility of the film by distribution in the hydrophobic segment of Eudragit RS100. Effects of both forms of the succinic acid could improve the hydration of Eudragit RS film. As a result, the permeability of the film was improved evidently. ConclusionThe lag time of famotidine time-controlled release pellets is induced by the hydrophobicity of the film. After water dissolve the organic acid, the dissociated and undissociated forms of succinic acid interact with the film through different ways. These interactions can change the structure of the film. Therefore the permeability of the film will be improved markedly.