Backgrounds: Quality of life related to oral health impact profile-14 (OHIP-14) is one of the important dimensions of quality of life. Since using narcotics or stimulants increases the incidence of periodontal diseases, we aimed to determine impact of Oral health-related quality of life in narcotic or stimulant addicts who referred to maintenance methadone therapy (MMT) centers in Ahvaz City, Iran.Methods: It was descriptive-analytical cross-sectional study which has conducted on 187 narcotic and stimulant addicts who referred to MMT centers in Ahvaz city; 2020. The data collection tools included the demographic variables and the standard OHIP-14 questionnaires. Descriptive statistics, independent t-test, one-way analysis of variance, and LMS test were run at the significance level of less than 0.05. Results: The mean and standard deviation of the participants' age was 36.03 ± 8.98 years. The quality-of-life scores related to oral health were 34.89 ± 6.50 totally as well as 37.37 and 33.96 in narcotic and stimulant addicts, respectively. The total quality of life related to OHIP-14 did not have a significant relationship with variables of age, life companions, level of education, number of children, economic status, employment status, insurance status, underlying disease, toothbrush use status, last dentist visit, and number of missing teeth (P> 0.05). However, a significant difference was found between the quality of life related to oral health based on the type of substance used (narcotic or stimulant), so that the mean quality of life related to oral health was higher in narcotic addicts than stimulant users (P <0.05). Conclusion: The quality of life related to OHIP-14 was more unfavorable in stimulant users than narcotic users. So, policy makers and authorities are required to focus their interventions and research programs to improve health-related quality of life in addicts, especially stimulant users.