Objectives: The aim of this research was to examine the knowledge, attitudes, and practices of pharmacists related to the impact of drugs and dietary supplements on laboratory test results. Participants and methods: The participants in this study were pharmacists from the Republic of Croatia. A cross-sectional study was conducted through an anonymous survey in May and June 2024. The survey was created as a Google form and consisted of 22 closed-ended questions. The survey collected data on the sociodemographic characteristics of the participants, as well as their knowledge, attitudes, and practices related to the impact of drugs and dietary supplements on laboratory test results. Results: A total of 144 individuals participated in the study. The majority (89.6%) were female. Most participants were younger, aged between 20 and 30 years, with shorter work experience ranging from 0 to 5 years. Most respondents (88.9%) completed a master's degree as their highest level of education, with the majority having studied in Zagreb (55.6%). It was observed that all participants believe it is essential for pharmacists to have knowledge of the impact of drugs and dietary supplements on laboratory test results, but most feel they lack sufficient knowledge on this topic and that it was not adequately covered during their studies. The study also revealed that participants are unaware of the large number of known interferences and do not fully recognize all the consequences or potential solutions for reducing these effects. Additionally, it was noted that most respondents believe patients should be informed about the potential impact and that they share the responsibility for patient education with laboratory professionals and doctors, although this is rarely practiced. The understanding of drug databases is also not at a satisfactory level, and their use in practice for informing about drug-test interferences is almost non-existent, despite most participants expressing a positive attitude toward their use. A positive attitude was also noted toward continuous education on drug and laboratory test interferences, as well as the use of automated systems that highlight these interferences. Conclusion: There are significant gaps in knowledge and dissatisfaction with the current education of pharmacists regarding drug/dietary supplement interferences with laboratory tests. In practice, these interferences are often neglected when informing patients about medications. Pharmacists have a positive attitude toward further education in this area and the use of automated clinical decision support systems. There is a need for improvement in pharmacists' education and communication practices, for an interdisciplinary approach, and the integration of digital tools to identify interferences and prevent subsequent clinical errors.