To find out what happens with a tablet, capsule or even an implant in the gut, it is essential to run dissolution tests (such as drug dissolution tests). Some products release the active compound directly in the stomach or upper small intestine. These dosage forms are called immediate release formulations. Others disintegrate at certain sections of the gut, e.g. enteric-coated dosage forms release the compound when entering the intestine. Extended release formulations release the compound constantly over the passage through the gut. In order to simulate the behaviour of such different dosage forms in the gut it is important to run formulation-based experiments in biorelevant media, such as FaSSIF, FeSSIF and FaSSGF. Biorelevant vitamin or drug dissolution and dosage form disintegration test results are then used to improve the formulation, or to establish IVIVC and to assess food effects. The following sections will show you the options of performing drug dissolution of different types of dosage forms.