Background: The rate of cardiovascular diseases in developing countries is approximately 60% and it is still has an increasing trend. The clinical effectiveness of aspirin in preventing cardiovascular events has been well proven. Although aspirin is an effective and inexpensive drug, its consumption is not equally beneficial for all patients. Many factors can be affective on the efficacy of antiplatelet drugs such as aspirin. Methods: This study was carried out on 260 patients who had stable angina pectoris and coronary artery disease was approved by coronary angiography. Based on opium addiction, the patients were divided into two groups. Opium addiction was diagnosed base on Diagnostic and Statistical Manual of Mental Disorders, fourth edition (DSM IV) criteria. The mid stream morning urinary sample were collected for measuring the urinary 11-dehydroxy thromboxane B2 level (UTXB2). Urinary level of UTXB2 was considered as an aspirin resistance index. Findings: The mean age of patients was 57.3 ± 8.9; and 44.6% of them were females. The aspirin resistance rate was 41.5%. Significant difference in aspirin resistance was observed between the opium addicts and non-addicts. (51.5% vs. 31.5%) (P = 0.001). The effects of confounding variables such as diabetes, hypertension, and hyperlipidemia were eliminated by regression logistic multivariable analysis. Conclusion: The prevalence of aspirin resistance in patients with stable angina pectoris was 41.5%. The prevalence of aspirin resistance in patients with stable angina pectoris who had opium addiction was significantly higher them non-addicts.