Nearly everyone at one time or another has been affected by an allergic disease, such as allergic rhinitis, urticaria or allergic rhinoconjunctivitis. Fortunately, these diseases can usually be controlled by instituting one or more of the following measures: allergen avoidance, pharmacotherapy or allergen immunotherapy. In addition to glucocorticoid nasal spray, the use of oral antihistamines is the quite common and such a treatment is available both on and off prescription. This study investigates common problems associated with oral histamines and reviews the efficacy and safety of the first and second generation antihistamines by analyzing pharmacists' cognitive service data at a regional hospital.