Diploma thesis title: Difference in the intensity of depression in patients treated with methadone replacement therapy compared to patients treated with buprenorphine replacement therapy. Objectives: The main objectives of this study were to compare the intensity of depression and scores on individual claims of the Beck Depression Inventory-II (BDI-II) questionnaire among patients treated with methadone replacement therapy and those treated with buprenorphine replacement therapy. Materials and methods: In the Mental Health Services at the Teaching Institute for Public Health of the Split-Dalmatia County in the period from March 18, 2021. to April 29, 2021. subjects treated with buprenorphine or methadone replacement therapy completed the Beck Depression Inventory-II (BDI-II) questionnaire. Also, data on patient general socio-demographic data, treatment data, risky behavior, and court problems were collected from Pompidou forms. Results: In this period, the study included 103 respondents, of whom 84 (81.6%) were male and 19 (18.4%) female. 47 subjects (45.6%) were treated with buprenorphine replacement therapy, while the remaining 56 (54.4%) were treated with methadone replacement therapy. Summarizing the results achieved by solving the Beck Depression Inventory-II (BDI-II) questionnaire, 50 respondents (48.5%) had minimal depression, 21 of them (20.4%) had mild depression, 16 (15.5%) had moderate depression, and the same number, 16 of them, had a severe form of depression., with no statistically significant differences among the study groups. There was a statistically significant (P<0.05) association of intravenous heroin consumption with an increased rate of overdose, more frequent HBV, HCV and HIV infections, more frequent violent behavior and breaking the law. Conclusions: The results of the study did not show statistically significant differences in the intensity of depression among patients treated with buprenorphine replacement therapy and those treated with methadone replacement therapy, nor statistically significant differences in score on individual claims of Beck Depression Inventory-II (BDI-II) questionnaires between these groups. However, hypotheses have been confirmed that patients treated with methadone or buprenorphine replacement therapy are mostly men, that patients who have consumed heroin intravenously are more prone to overdose, more likely to develop HBV, HCV and HIV infections and are prone to violent behavior and breaking the law.