BACKGROUND Many of lay person believe that opium lowers blood glucose. However some studies show the opposite results. In this study, we tried to evaluate the effect of opium on blood glucose and insulin resistance. METHODS This comparative study including 53 addicts in case groups who used opium just in the form of smoking and 55 non-addicts in a control group, took part in the study, after proving not to be opium users. After taking blood samples, their fasting blood glucose (FBG), fasting blood insulin and lipid profiles were evaluated. Furthermore, insulin resistance index was analyzed via the homeostatic model assessment of insulin resistance (HOMA-IR) formula with the cut-off points of 7.2 and 7.1. FINDINGS Age and gender were not significantly different between the groups. There was no significant difference regarding the prevalence of insulin resistance between the two groups, according to the cut-off points of 7.1 and 7.2 (P = 0.196 and P = 0.248, respectively). Mean insulin resistance index was not significantly different between the two groups (P = 0.325). In the case group, fasting blood insulin was considerably lower (P = 0.025) and fasting blood sugar (FBS) was significantly higher (P = 0.016) than the control group. CONCLUSION According to the level of insulin and FBS in addicts, it does not seem that opium has a significant effect on reducing the blood glucose and insulin resistance.