Objectives The primary objective of the research is to determine the impact of a clinical pharmacist’s intervention on the adherence of chronic patients on discharge from the hospital. The specific objectives are to determine the most common causes of non-adherence in chronic patients, to determine the frequency and type of therapeutic problems in chronic patients, to determine the acceptance of clinical pharmacist intervention by physicians and to determine the type and frequency of different categories of drug interactions. Patients and methods This intervention study was conducted at the Clinic for Internal Medicine with a dialysis center within the University Clinical Hospital Mostar for two months. One hundred patients were included in the research. For the purpose of data collection, a survey questionnaire and a structured interview with the patient were used. The pharmacist had an insight into the patient's card, prescribed therapy, diagnoses and laboratory findings. The survey and structured interview were conducted with patients who agreed to participate in the study and signed informed consent. One of the criteria for inclusion in the study was a stay in the hospital for at least one night. Patients were randomized into two groups of 50 subjects, one interventional group and the other control group. From the patient's medical record were obtained data on age, sex, diagnoses, prescribed medications and laboratory test results. In the intervention group of patients, upon discharge from the hospital, the clinical pharmacist reviewed the prescribed therapy and conducted a structured interview with the patient. Before the interview, a data analysis of the prescribed pharmacotherapy was performed and the present therapeutic problems were identified. The structured interview included collecting data on dietary supplements and OTC drugs currently used by the patient, educating patients about the goals and ways to monitor the success of therapy, the importance of adhering to prescribed therapy and giving clear instructions on the proper use of certain drugs. The Lexi-comp database, the Summary of Product Characteristics and other available professional literature were used to prepare the proposed intervention. The proposal of the pharmaceutical intervention contained a literature citation, on the basis of which a certain intervention was proposed. Re-interview with patients was scheduled within 30-60 days after discharge. In the re-interview, patients were asked 8 questions from the Morisky Adherence Scale. The control group consists of 50 patients who came to the hospital for a check-up and who were not interviewed by a clinical pharmacist at discharge. All patients from the control group were also asked, 8 questions from the Morisky adherence scale. Results 203 therapeutic problems were identified by pharmacist. 91 types of drug-drug interactions were found. Interactions of clinical grade C and D were the most common and accounted for 44% of identified therapeutic problems. Contraindication or interaction of the degree of clinical significance X was observed in 2 patients and accounts for 1% of therapeutic problems. Drug-food interactions were found in 18% of patients, drug-supplement interactions were found in 6% of patients, drug-drug interactions were found in 10% of patients. Duplication of therapy was found in 2% of patients, in 1% of patients side effects of the drug were observed. Misunderstanding of the drug dosing schedule was found in 10% of patients. Drug-dietary drug interactions were found in 12 patients. Inadequate dosing interval was observed in 3% of patients, the absence of a clear indication for drug use was found in 3% of patients, duplication of therapy was found in 2% of patients. Non-prescribing of the drug despite the existence of an indication for the use of the drug was noted in 0.5% of patients. A total of 151 therapeutic problems were identified that required patient-directed pharmacist intervention. All patients (100%) of the intervention group were given advice on the correct dosage and effect of the drugs prescribed to them in therapy. Drug-food interaction was observed in 24% of the patients in the intervention group, and the dosing schedule of daily therapy was developed in 19% of the subjects. 8% of patients were informed about the drug-supplement interaction, 7% of patients were given a table for monitoring blood pressure, and 3% of patients were given tables for monitoring blood sugar. Informing the patient about possible side effects of the drug was performed in 6% of patients. 1% of patients were referred to re-examination. A total of 52 therapeutic problems were identified that required a physician-directed pharmacist intervention. Of the proposed interventions, the most common are informing physicians about interactions (35%), discontinuing the drug (25%), referring to enhanced monitoring (21%), changing the dosing interval (13%), replacing one drug with another (6%), informing about combinations more active substances in one tablet (2%), introduction of a new drug into therapy (2%), change of drug dose (2%). Out of a total of 52 physician-directed pharmacist interventions, 46 or 88.5% were accepted (Figure 2). 6 or 11.5% of total interventions were rejected. The largest number of patients in the intervention group showed moderate adherence, 56%, while 26% of patients showed high adherence, and 18% of patients showed poor adherence. The most common cause of inadequacy is the burden of patients with prescribed therapy, i.e. 82% of patients answered YES to question no. 7 of Morisky scale. The largest number of patients in the control group showed moderate adherence, 52%, while 38% of patients showed poor adherence, and 10% of patients showed high adherence. The most common cause of non-adherence of the control group (80%) is also the burden of patients with prescribed therapy. Conclusion A total of 203 therapeutic problems were identified in this study, of which drug interactions accounted for 44.8%. 52 physician-directed pharmacist interventions were performed, 88.5% of them were accepted. A total of 151 therapeutic problems were identified that required patient-directed pharmacist intervention. The largest number of patients in the intervention group showed moderate adherence (56%), and a very similar percentage of moderate adherence was in the control group (52%). However, the big difference is in the percentage of high and low adherence. Namely, 26% of the patients in the intervention group showed high adherence, and 18% of the patients showed poor adherence. While the percentage of highly adherent in the control group is 18%, and poorly adherent is significantly higher compared to the intervention group, as much as 38%. The most common cause of inadequacy of both groups is the burden of patients with prescribed therapy or a large number of drugs in therapy. In this study, greater adherence was shown in subjects in whom a clinical pharmacist had an intervention after discharge from the hospital. However, further research is needed on a larger sample and over a longer period to monitor the effects of clinical pharmacist interventions on patient adherence after discharge, improvement of therapeutic outcomes and pharmacoeconomic effects of such interventions.