Modern therapy has changed the way diseases are controlled and has brought significant benefits. In spite of all the benefits, adverse drug reactions are a common, often preventable, cause of illness, disability and even death. Besides the intrinsic danger associated with the drug, patients might have a particular, unpredictable hypersensitivity to certain drugs, which requires careful monitoring. Different studies have shown that adverse drug reactions related hospital admissions comprise up to 10% of the total number of hospitalizations. Adverse drug reactions can be difficult and sometimes impossible to distinguish from the patient's disease as they act through the same physiological and pathological pathways. Unrecognized adverse drug reactions inflict health damage, hospital costs and may lead to prolonged hospitalization. The purpose of this paper is to review and clarify some specific terminology and to assess the likelihood that a suspected adverse drug reaction is actually due to a medicine, by outlining the information needed for recognizing an adverse drug reaction and the steps of a causality assessment of a theoretical drug-induced case of pancreatitis.