Abstract: The invention relates to a process for preparing an active-principle-containing adhesive formulation for use in a transdermal therapeutic system, comprising the following steps: a) providing an adhesive formulation containing a carboxylic acid ester-based solvent and a self-adhesive polymer matrix containing monomers of the compounds on which the polymer matrix is based, b) removing the carboxylic acid ester-based solvent and the monomers from the adhesive formulation, c) re-dissolving the compound obtained in step b) in an organic solvent that does not contain any ester groups, and adding a pharmacologically active principle having at least one hydroxyl group, carboxyl group, amino group and/or ester group so that the active-principle-containing adhesive formulation is obtained. The invention also relates to a transdermal therapeutic system containing the active-principle-containing adhesive formulation.