Introduction:The prescription and costs of antiulcer medications for in-hospital use have increased during recent years with reported inadequate use and underused.Aim: To determine the patterns of prescription-indication and also perform an economic analysis of the overcost caused by the non-justified use of antiulcer medications in a third level hospital in Colombia.Materials and methods: Cross-sectional study of prescription-indication of antiulcer medications for patients hospitalized in "Hospital Universitario San Jorge" of Pereira during July of 2012. Adequate or inadequate prescription of the first antiulcer medication prescribed was determined as well as for others prescribed during the hospital stay, supported by clinical practice guidelines from the Zaragoza I sector workgroup, clinical guidelines from the Australian Health Department, and finally the American College of Gastroenterology Criteria for stress ulcer prophylaxis. Daily defined dose per bed/day was used, as well as the cost for 100 beds/day and the cost of each bed/drug. A multivariate analysis was carried out using SPSS 21.0.Results: 778 patients were analyzed, 435 men (55.9 %) and 343 women, mean age 56.6 ± 20.1 years. The number of patients without justification for the prescription of the first antiulcer medication was 377 (48.5 %), and during the whole in-hospital time it was 336 (43.2 %). Ranitidine was the most used medication, in 438 patients (56.3 %). The cost/month for poorly justified antiulcer medications was € 3,335.6. The annual estimated cost for inadequate prescriptions of antiulcer medications was € 16,770.0 per 100 beds.Conclusion: A lower inadequate prescription rate of antiulcer medications was identified compared with other studies; however it was still high and is troubling because of the major costs that these inadequate prescriptions generates for the institution.