PROBLEM TO BE SOLVED: To provide a sustained release preparation and its dispersing medium, capable of suppressing the initial release of a physiologically active substance directly after its administration and releasing a constant amount of the physiologically active substance for a long period of time. SOLUTION: This sustained release preparation and its dispersing medium, capable of suppressing the initial release of a physiologically active substance directly after its administration and releasing a constant amount of the physiologically active substance for a long period of time is obtained by adding a cationic substance or polyols to the outside of a matrix or its dispersing medium.
