Teaching the molecular aspects of drug-target interactions and selectivity is not always an easy task. In this context, the use of alternative and engaging approaches could help pharmacy and chemistry students better understand this important topic of medicinal chemistry. Herein a 4 h practical exercise that uses freely available software as a tool to teach the drug-target interaction process is described. This exercise is designed as a comparative approach based on the distinct cyclooxygenase 2 (COX2) affinities of ibuprofen and celecoxib. Students learn how to find crystallographic structures in free protein databases online and how to treat the raw crystallographic data. Thus, students learn how to analyze the drug arrangement on the active site, looking for areas that are related to the molecular recognition process. At the end of the class, students summarize all of the molecular requirements related to drug-target interactions and selectivity. Additionally, students visualize three-dimensionally the structure-activity relationship of ibuprofen and celecoxib.