The invention relates to an oral dosage form, comprising at least one biologically active agent, formulation auxiliary substances and magnetizable particles, wherein the dosage form has an at least two phase composition, wherein the phases can dissolve in the body after oral administration due to their formulation and the magnetizable particles are bound in formulation auxiliary substances and are present in a magnetized state, wherein the magnetized particles are present in at least two phases of the dosage form and generate magnetic fields, wherein these phases dissolve at different times in the body after oral administration, and wherein the magnetic field strength with respect to time, position and movement in the body is acquired using a detection system and can be evaluated using a computer-based evaluation system.