To provide a method for producing a preparation for a medicine, capable of protecting one or plural active medicine components from oxidation decomposition and consequently facilitating a long-team preservation of the preparation.

This method controls oxidation decomposition of a preparation for a medicine containing at least one readily oxidizable active medicine component. The method comprises adding an iron (II) ion source preferably in a state of an excipient for a medicine in an amount to control oxidation to the preparation. The preparation for a medicine comprises at least one readily oxidizable active medicine component and an iron (II) ion source in an amount to control oxidation preferably in a state of an excipient for a medicine. The use of the iron (II) ion source in the preparation for a medicine as an antioxidant is provided.