Changes in the psychological defense mechanism and clinical features of patients with OCD – A four-year follow-up study

•Follow up with 4-year changes in the efficacy outcome, defense style questionnaire (DSQ) score, and clinical features of patients with obsessive-compulsive disorder (OCD).•Analyze the relationship between different levels of efficacy and changes in the patients' psychological defense mechanisms.•An abnormal psychological defense mechanism plays an important role in OCD, and the use of a mature defense mechanism is significantly related to the treatment efficacy.