The medico-legal and economic burden of adverse drug events has been estimated in the billions of dollars of which true drug hypersensitivities represent about a third of all adverse drug reactions. Clinicians and patients often mislabel adverse drug reactions as drug allergies or hypersensitivities thus compromising the use of certain proven medications. The primary objective of this research project is to determine the prevalence of false drug allergy histories in hospitalized patients. This objective will be assessed by: (1) reviewing on a daily basis all medication administration records with documented patient reported drug allergy histories, (2) discerning true allergies by using the validated method of Naranjo et al. This method is used to classify drug allergies into four categories: definite, probable, possible and doubtful. The study will enroll five hundred patients from 2 different hospitals. The long term research goal is to influence clinicians and care givers to implement appropriate measures to prevent erroneous reporting of drug allergies by ensuring detailed medication histories and thus decreasing medical costs and optimizing drug therapies. Pharmacists and other health care providers can play a key role in discerning true allergy and in educating patients on the difference between an allergic and an adverse drug effect in order to prevent patients from reporting unfounded allergic reactions in the future.