Introduction: Obsessive-compulsive disorder (OCD) is one of the most common and debilitating diseases. Approximately 40-30% of these patients are resistant to treatment, which auxiliary drugs are used to treat these patients. One of these drugs is caffeine, which is capable of affecting adenosine receptors and interfering with its release and serotonin reuptake. Considering the limitations of previous studies in this area, including lack of control group, this double-blind study compared the effectiveness of caffeine in the management of patients with treatment-resistant OCD in comparison with placebo group. Materials and Methods: 62 patients who referred to the psychiatric clinic of Imam Hossein Hospital in Tehran from 2017 to 2018 were enrolled in the study. According to the psychiatrist's interview, patients with OCD were selected randomly in two groups including caffeine and placebo, after having met the criteria for inclusion and obtaining informed consent. Patients were followed for 8 weeks and compared in terms of the severity of OCD before and after intervention using YBOCS questionnaire. Results: The two groups of treatment and control were similar in terms of study variables (gender, age, education, age, comorbidity). The mean Yale-Brown Obsessive Compulsive Scale (Y-BOCS) in the treatment and control groups before intervention were determined to be 27.16 and 25.4, respectively, which changed to 24 and 27.23 after medication intervention, which exhibited a decrease of about 3 points (12%) in the treatment group, and was statistically significant based on linear regression analysis ( P = 0.009). Considering other variables, the effect of caffeine was still statistically significant in the two groups. Conclusion: Based on the findings of our study, caffeine can reduce the severity of the symptoms of OCD and serve as an auxiliary treatment for OCD.