Background: Nowadays, substance use has increased substantially. Substance has been a major social problem in Iran for many years. Addressing the substance use problem requires a thorough understanding of the dimensions and pattern of substance use. This study aimed to find a pattern of opium use, as the most frequently used opioid in Iran. Materials and Methods: In this cross-sectional study, data were collected using a researcher-made questionnaire. After confirming the validity and reliability total number of 2018 patients participated in the study. Descriptive statistics including mean, median, and standard deviation were used for data analysis. In addition, SPSS 16 was used to analyze event and time-to-event data, and the hazard and survival functions (using cox regression). Results: Our study results showed that of the 1788 (88.60%) participants who were using opium, as the main substance, with other substances, 87 were women and 1701 were men. Moreover, the Median age of opium use initiation among the total population (both genders) was 22 years. Thus,there was a statistically significant difference in the Median age of opium use initiation between men and women (p 0<0.05). The analysis of substance use by people born in different decades showed that the age of opium use initiation had a declining trend. In addition, there was a significant difference in the Median age of opium use initiation between the people born in different decades (p 0<.05). Conclusion: Opioid prevention education at an early age, i.e. in adolescence and even in childhood is essential.