A lot of drugs can induce hypomagnesemia as side effect. On the other hand, magnesium deficiency may be a risk factor for digitalis and drugs known to prolong the QT-interval and thus favour the development of torsades-de-pointes tachycardias. Controversely, the indication for most oral magnesium supplements in Germany is: proven magnesium deficiency if this is the cause for muscular troubles (neuromuscular disturbances, calf cramps). Due to this cutback magnesium attracts poor attention in clinical practice and the determination of serum magnesium concentrations is seldom ordered. Moreover, the lower level of the reference range for serum magnesium is often kept too low. As a consequence hypomagnesemia as side effect remains frequently undetected.