PROBLEM TO BE SOLVED: To provide a transdermal therapeutic system (TTS) with improved stability, in which reactions with hydroperoxides are reduced, and a method for producing the same.SOLUTION: In the production of a TTS containing one or two or more oxidation susceptible active substances, ingredients substantially free from hydroperoxides are used as constituents of the formulations thereof. More specifically, the sum of the peroxide numbers (PON), exhibited by the constituent parts of the formulations which contain the active ingredient(s) is 20 or less, preferably 10 or less, and particularly preferably 5 or less.
