Potentially inappropriate prescribing is a common problem, especially in elderly care. To tackle this problem, Irish medical experts have developed a list of criteria when medication should be added or omitted based upon the patient's physical condition and medication use, known as the STOPP and START criteria. The STOPP and START criteria have been formulated to identify the prescribing of potentially inappropriate medicines (PIMs) and potential prescribing omissions (PPOs). One of the most common problems of inappropriate prescribing is gastro-intestinal track bleedings. For this purpose, nine of the 87 STOPP and START criteria are designed to prevent this. However, the prevalence of gastro-intestinal track bleedings has not been established when these nine STOPP and START criteria are violated. The database contained 182,000 patients belonging to 49 general practitioners in the region of Amsterdam, The Netherlands. We estimated both the incidence of PIMs and PPOs and whether harm, in this case a gastro-intestinal track bleeding, occurred. We found that although violation of the nine STOPP or START criteria were possibly associated with harm (OR = 1.30), this association was not statistically significant (p = 0.323). Searching for evidence for harm informs decision support design aimed at improving quality of medication prescription as it prioritizes the many suggested criteria based on their relevance.