Satar Rezaei,1 Mohammad Hajizadeh,2 Sina Ahmadi,3 Mohammad Ebrahimi,4 Behzad Karami Matin1 1Research Center for Environmental Determinants of Health, Health Institute, Kermanshah University of Medical Sciences, Kermanshah, Iran; 2School of Health Administration, Faculty of Health, Dalhousie University, Halifax, NS, Canada; 3Department of Social Welfare Management, University of Social Welfare and Rehabilitation Sciences, Tehran, Iran; 4Student Research Committee, Kermanshah University of Medical Sciences, Kermanshah, IranCorrespondence: Behzad Karami Matin Research Center for Environmental Determinants of HealthHealth Institute, Kermanshah University of Medical Sciences, Kermanshah, IranTel +98 83 38264164Postal code +98- 6719851351 Email bkmatin1344@gmail.comBackground: Self-medication (SM) is a public health concern globally. This study aimed to measure socioeconomic inequality in SM and identify its main determinants among Iranian households.Methods: A total of 38,859 households from the 2018 Household Income and Expenditure Survey (HIES) were included in the study. Data on SM, household size, age, gender and education status of the head of household, monthly household’s expenditures (as a proxy for socioeconomic status), health insurance coverage and living areas and provinces were obtained for the survey. The concentration curve and the normalized concentration index (Cn) were used to quantify the magnitude of socioeconomic inequality in SM among Iranian households. The Cn was decomposed to identify the main determinants of socioeconomic inequality in SM in Iran.Results: The results indicated that 18.2% (95% confidence interval [CI]: 17.7% to 18.5%) of households in Iran had SM practice in the past month. The results suggested a higher concentration of SM among the rich households (Cn= 0.0466; 95% CI= 0.0321 to 0.0612) in Iran. The concentration of SM among high SES households was also found in urban (0.0311; 95% CI=0.0112 to 0.0510) and rural (= 0.0513; 95% CI=0.0301 to 0.0726) areas. SM was concentrated among the rich households in Tehran, Qom, Esfahan, Ardebil, Golestan, and Sistan and Baluchestan provinces. In contrast, a higher concentration of SM was found among the poor households in Semnan, North Khorasan, Kerman, Bushehr, and South Khorasan provinces. The decomposition revealed SES of household, itself, as the main contributing factor to the concentration of SM among the wealthy households.Conclusion: This study demonstrated that SM is more concentrated among socioeconomically advantaged households in Iran. Thus, effective evidence-based interventions should be implemented to improve awareness about SM and its negative consequences. Further studies are required to investigate the consequences of SM practice among people.Keywords: self-medication, inequality, socioeconomic status, Iran