Abstract Background In recent years, lung cancer (LC) incidence has increased in Iran. The use of opium and its derivatives (O&D) has increased as well. This study aimed to investigate the association between the use of O&D and LC incidence. Methods In this case-control study conducted in Kerman, Iran; 140 patients with lung cancer and 280 healthy controls matched by age, sex, and place of residence were included. Data, including O&D use, cigarette smoking, alcohol use, and diet, were collected using a structured questionnaire. The relation between the use of O&D and LC was evaluated using conditional logistic regression adjusted for tobacco smoking, education, daily intake of fruit, vegetables, red meat, and hydrogenated fats. Results Opium ever-use was associated with an increased risk of LC (Adjusted Odds Ratio (AOR) =5.95, 95% CI: 1.87–18.92). Participants were divided into low and high use groups based on the median of opium use in the control group. A significant dose-response relation was observed between the amount of daily O&D use and LC; and the relation was stronger in high users (AOR low users = 3.81% CI: 1.13–12.77 and OR high users = 9.36, 95% CI: 2.05–42.72). Also, LC was higher among participants starting the use of O&D at younger ages (≤ 41 years old vs never users AOR = 8.64, 95% CI: 1.90–39.18) compared to those who started at an older age (> 41 years old vs never users, AOR = 4.71, 95% CI: 1.38–16.08). The association between opium, and lung cancer among non-smokers was OR: 6.50 (95% CI: 2.89 to 14.64). Conclusion The results of this study show that opium use is probably a dose related risk factor for lung cancer.
