The aim of stability testing lies in its possibility of revealing all the effects that may influence the quality, efficacy and safety of a pharmaceutical preparation. The stability of a dosage form means that the release of the active ingredients remains unchanged or within specific limits. The manner of stability testing is regulated by guidelines, which consist of -- besides the regular tests of the active ingredient and the degradation products, the concerning impurities, the water content, the hardness -- the dissolution tests. Most physical changes influence the drug release in vivo, which can -- in vitro -- be followed by dissolution.