1. An oral dosage form, comprising a biologically active agent, a formulation auxiliary substance and magnetizable particles, wherein the dosage form has a composition of at least two phases, wherein the phases can dissolve in a body after oral administration and wherein the magnetizable particles are bound in the formulation auxiliary substance and are present in a magnetized state, wherein the magnetizable particles are present in at least two phases of the dosage form and generate magnetic fields, wherein at least two of the magnetic fields have different alignments, wherein the phases dissolve at different times in the body after oral administration, and wherein a magnetic field strength with respect to time, position and movement in the body can be acquired using a detection system and can be evaluated using a computer-based evaluation system.