Comparison of Theory of Mind between Patients with Major Depressive Disorder and Stimulant-Induced Depressive Disorder

Objective: Theory of mind (ToM) denotes the ability to understand the mental state of others and perceive their unique beliefs and emotions. In this study, we compared ToM between individuals with major depressive disorder (MDD) and stimulant-induced depressive disorder (SIDD). Method: This cross-sectional, causal-comparative study included patients with MDD or SIDD admitted to Ostad Moharary Neuropsychiatric Hospital between January and June 2022. Each diagnosis was confirmed through a semi-structured interview conducted by a single attending psychiatrist according to the DSM-5 criteria. After consecutive sampling of 110 individuals, 51 patients completed the study in each group. Demographic characteristics were recorded, and the Persian version of the revised Reading the Mind in the Eyes Test (RMET) was used to evaluate ToM. Statistical analysis was performed using SPSS v.25, employing the t-test, chi-squared test, linear regression, and analysis of covariance (ANCOVA). Results: Our analysis included 102 subjects (65.7% male) with a mean age of 35.17 ± 7.54 years. The two groups were similar in age, gender, marital status, working status, occupation, economic class, and ethnicity (P > 0.05). The RMET scores were 12.94 ± 4.03 and 11.86 ± 3.15 in the MDD and SIDD groups, respectively (P = 0.135). Almost all patients had low RMET scores (< 22); only two individuals in the MDD group achieved normal scores (22–30). ANCOVA revealed no significant confounding effects between the independent variables. Furthermore, regression analysis revealed that the level of education had a significant linear relationship (β = 0.249) with the RMET score (P = 0.021). Conclusion: Hospitalized patients with MDD and SIDD have similar ToM deficits, as measured by the RMET.