Background/purpose: The electronic clinical decision support system (CDSS) is mainly used to assist health care providers in their decision-making process. CDSS includes the dose range checking (DRC) tool. This study aims to evaluate the clinical validity of the DRC tool and compare it to the institutional Formulary and Drug Therapy Guide powered by Lexi-Comp. Methods: This retrospective study analyzed DRC alerts in the inpatient setting. Alerts were assessed for their clinical validity when compared to recommendations of the institution’s formulary. Relevant data regarding patient demographics and characteristics were collected. A sample size of 3000 DRC alerts was needed to give a margin of error of 1% (using normal approximation to binomial distribution gives 30.26/3000 = 1%). Results: In our cohort, 1659 (55%) of the DRC alerts were generated for adult patients. A total of 1557 (52%) of all medication-related DRC alerts recommended renal dose adjustments, while 708 (24%) needed hepatic dose adjustments. Majority of alerts, 2844 (95%), were clinically invalid. A total of 2892 (96%) alerts were overridden by prescribers. In 997 (33%) cases, there was an overdose relative to the recommended dose, and in 1572 (52%) there was underdosing. Residents were more likely to accept the DRC alerts compared with other health provider categories ( P < .001). Conclusion: Using DRC as a clinical decision support tool with minimal integration yielded serious clinically invalid recommendations. This could increase medication-prescribing errors and lead to alert fatigue in electronic health care systems.