Background Critically ill patients treated in the intensive care units (ICUs) often suffer from side effects and drug-related problems (DRPs) that can be life-threatening. A way to prevent DRPs and improve drug safety and efficacy is to include clinical pharmacists in the clinical team. This study aims to evaluate the classification of drug-related problems and the implementation of clinical pharmacy services by a clinical pharmacist in the ICU of a university hospital in Turkey. Methods This study was carried out prospectively between December 2020 and July 2021 in Gazi University Medical Faculty Hospital Internal Diseases ICU. All patients hospitalized in the intensive care unit for more than 24 h were included in the study. During the study, the clinical pharmacist's interventions and other clinical services for patients were recorded. DRPs were classed according to the Pharmaceutical Care Network Europe V.8.02. Results A total of 151 patients were included during the study period corresponding to 2264 patient-days. Patients with DRPs had a longer hospital stay and a higher mortality rate (p < 0.05). 108 patients had at least one DRP and the total number of DRPs was 206. There was an average of 1.36 DRPs per patient, 71.5% of patients experienced DRP and 89.22 DRPs per 1000 patient-days. A total of 35 ADEs were observed in 32 patients. ADE incidence was per 1000 patient-days 15.45. ADEs were caused by nephrotoxicity (48.57%), electrolyte disorders (17.14%), drug-induced thrombocytopenia (17.14%), liver enzyme increase (8.57%) and other causes (8.57%). Drug selection (40.29%) and dose selection (54.36%) constituted most of the causes of DRPs. Dose change was the highest percentage of planned interventions with a rate of 56.79%. Intervention was accepted at a rate of 90.8% and it was fully implemented. Conclusion In this study, the importance of the clinical pharmacist in the determination and analysis of DRPs was emphasized. Clinical pharmacy services like the one described should be implemented widely to increase patient safety.