Until now drug therapy has primarily been controlled by dose titration on the basis of effects and side effects. However, a lot of people being treated with a drug experience too little effect or too many side effects. Therefore it will be advantageous to improve drug therapy and make it even more "individualized". In this chase metabolomics is a hot topic. The aim of this paper is to review the concepts of metabolomics and the possible applications in regard to drug development, drug therapy and diagnosis, prognosis and monitoring of diseases.