Background & Objectives: Obsessive–compulsive disorder (OCD) is one of the most common, debilitating, and resistant psychological disorders. The core symptoms of patients with OCD are their inability to inhibit intrusive thoughts and images, and repetitive, stereotyped behaviors. Given the prevalence and seriousness of the consequences of OCD on various aspects of the social, individual, and family lives of people with this disorder and the significant role that brain–behavioral and self–control systems play in the persistence and resistance to treatment of this disorder, examining applied psychological therapies is helpful for therapists in identifying more effective treatment methods for treating these individuals. Given that biological and complementary therapies for patients with OCD have not been able to provide complete recovery from this disease, the use of psychological therapies to change schemas and mindfulness, attitude towards oneself and the surrounding world, and increase adaptive responses seems necessary. Therefore, the present study was conducted to compare the effectiveness of schema therapy and mindfulness on the brain–behavioral and self–control systems of patients with OCD.

Methods: The present study used a quasi–experimental, pretest–posttest design with a control group. The statistical population of the study included all patients with OCD living in the city of Sari, Iran. People with OCD who were referred to 4 counseling centers in Sari between August and October 2024 were invited to participate in this study. Using a purposive sampling method, 45 eligible volunteers entered the study through a diagnostic interview, based on the study's inclusion and exclusion criteria. Then they were randomly assigned to three groups of 15 people each. The inclusion criteria for the study were as follows: diagnosis of OCD based on the Structured Clinical Interview for DSM–5 (SCID–5) conducted by a specialist psychologist, and the individual scoring higher than 15 on the Maudsley Obsessional–Compulsive Inventory (MOC; Hodgson & Rachman, 1977); having a history of obsessions for at least 6 months and a maximum of 5 years; minimum educational level of a high school diploma; willingness to attend all treatment sessions; lacking received treatment for obsessions in the last 3 months; absence of psychotic disorders, bipolar I disorder, severe personality disorder, severe depressive disorder, and substance abuse disorder, which were assessed through a structured clinical interview based on SCID–5. The exclusion criteria were as follows: unwillingness to continue cooperating in the study, receiving concurrent psychological interventions, receiving concurrent pharmacological interventions, and missing more than two sessions. In this research, the first experimental group received schema therapy; the second, mindfulness therapy; and the control group received no intervention until the end of the study. To address ethical concerns, the control group received the more effective treatment after the end of the study. All three groups completed the research questionnaires as a pretest and posttest. Data analysis was performed in two sections: descriptive statistics and inferential statistics in SPSS software version 24. At the descriptive level, frequency, percentage, mean, and standard deviation were used. At the inferential level, univariate analysis of covariance and Bonferroni post hoc tests were used at the 0.05 significance level.

Results: The results showed a significant difference between the schema therapy and mindfulness groups and the control group on the variables of behavioral inhibition system (p = 0.001), behavioral activation system (p = 0.001), and self–control (p = 0.001). Also, schema therapy was more effective than mindfulness in increasing behavioral inhibition system (p = 0.005) and self–control (p = 0.005), and in reducing the behavioral activation system (p = 0.005) in patients with OCD.

Conclusion: Based on the findings of the study, schema therapy is more effective than mindfulness in increasing the behavioral inhibition system and self–control and reducing the behavioral activation system in patients with OCD.