FIELD: medicine, pharmacy. SUBSTANCE: invention relates to stable peroral pharmaceutical composition and to its preparation where alterations of medicinal agent releasing are prevented at storage under conditions of light effect by addition of yellow ferric (III) oxide and/or red ferric (III) oxide to the preparation with prolonged release of matrix type and comprising medicinal agent, hydrophilic base and polyethylene oxide. Invention relates also to method for prevention of alterations in releasing medicinal agent at storage of preparation with prolonged release of matrix type and comprising medicinal agent, hydrophilic base and polyethylene oxide under conditions of light effect. Invention provides increasing the guaranteed time for product storage and to enhance quality of product. EFFECT: improved preparing method, valuable pharmaceutical properties of composition. 21 cl, 1 tbl
