According to the National Health Insurance Service’s 2023 report, the number of first-time patients diagnosed with depression, bipolar disorder, and schizophrenia among individuals in their 20s was 69,333 in 2018, 84,139 in 2019, 102,990 in 2020, 120,017 in 2021, and 128,582 in 2022 [1]. This age group recorded the highest number of initial consultations across all age groups over the past 5 years. Furthermore, statistics from Statistics Korea in 2022 indicated that the number of suicides was 12,906, with a suicide rate of 25.2 per 100,000 people. The leading cause of death for individuals from their 10s to their 30s was suicide [2]. These statistics highlight the severe issue of depression and suicide rates in Korea.

Given this context, many studies have focused on the mental health of young adults, especially on the close relationship between depression and suicide. According to the Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition (DSM-5), frequently or recurrent thoughts of death, suicidal ideation, suicide attempts, or plans for suicide are major symptoms of depression [3]. A domestic cohort study on depression involving 723 patients who visited hospitals for depression treatment reported that 19.8% had attempted suicide at least once in the past, and approximately 70% experienced suicidal thoughts during the study period [4]. Among mental disorders, depression had the highest suicide rate, with 364.4 suicides per 100,000 discharged patients within 30 days post-discharge [5]. Individuals who attempted suicide once had a 6.5 times higher risk of experiencing major depressive disorder (MDD) over their lifetime, while those with two or more attempts had a 7.9 times higher risk [6]. Previous studies have reported that most individuals who commit suicide exhibited depressive symptoms at the time, indicating a significant correlation between depression and suicide [7,8].

Depressed patients also exhibit differences in cognitive characteristics. Compared to control groups, individuals with MDD have been shown to perform worse on the Wechsler Adult Intelligence Scale (WAIS), with lower performance IQ and significantly poorer processing speed [9,10]. Studies have also explored the impact of cognitive and psychological characteristics [11] and the severity of cognitive deficits in young adults with MDD [12].

Research on the Korean Reasons for Living Inventory (KRFL), a measure investigating the belief systems of individuals at risk for suicide but who have not attempted suicide, shows that reasons for living (RFL) directly inhibits suicidal behavior. According to Rietdijk et al. [13], one of the six subcategories of the K-RFL, “survival and coping beliefs,” is a significant factor. The categories include survival and coping beliefs, responsibility to family and child-related, fear of death and social disapproval, future expectations. Individuals with lower scores in these areas are approximately 7 times more likely to engage in self-harm or suicidal behavior compared to those with higher scores. This finding aligns with studies demonstrating the moderating effect of RFL on the relationship between various independent variables and suicidal thoughts [14-17].

Lindenmayer et al. [18] noted that symptoms of mental disorders affect various life domains, including daily activities, family life, social relationships, and occupational functioning, and that overall functional impairment is associated with cognitive deficits [19]. Persistent cognitive impairments lead to negative outcomes in adaptive functioning and increase the risk of recurrence [20,21]. This underscores the importance of addressing cognitive deficits as a critical health factor in adults with MDD. Consequently, identifying cognitive impairments is crucial for the therapeutic management of mental disorders [22]. Hence, there is a growing need for special attention to the psychopathology of attempters and for individualized and proactive clinical approaches to prevent the recurrence of suicide attempts [23]. Studying the psychological characteristics of suicide attempters can effectively identify the risk factors leading to suicide attempts [24].

What accounts for the psychological differences between suicide attempters and non-attempters among depressed patients? The Minnesota Multiphasic Personality Inventory-2 (MMPI-2) comprises numerous subscales that evaluate a wide range of symptoms and clinical characteristics related to mental disorders, including items assessing suicidal ideation [25]. Comparing the mean MMPI-2 scores between the attempter and non-attempter, it is reported that the attempters show higher scores on scales measuring suicidal thoughts, sadness, depression, feelings of inadequacy, and guilt. This suggests that the suicide attempters perceive their depression more severely than the non-attempter [24].

Existing studies have analyzed MDD patients and suicide attempters using the MMPI-2 and RFL. However, studies that comprehensively compare cognitive and psychological characteristics, including cognitive function, remain limited. Additionally, most previous studies have focused on adolescents or patient populations without age distinctions, resulting in a lack of research specifically focusing on young adults-a population characterized by difficulties in emotional regulation, heightened vulnerability to stress and impulsivity, and a relatively high suicide rate compared to other age groups. Given that young adulthood is a critical period for mental health intervention, understanding the psychological and cognitive characteristics of this group is essential for developing effective suicide prevention strategies. Therefore, this study aims to provide a comprehensive understanding of the psychological characteristics of young adults with MDD.

Based on these findings, this study aims to verify the differences in RFL, cognitive functions, and psychological characteristics among three groups: attempters and non-attempters within the depressed patient population, and healthy controls (HCs). This study seeks to provide a multifaceted perspective on suicide attempts and contribute to appropriate therapeutic interventions.

This study aimed to examine the impact of suicide on patients with depression, and it was revealed that there were differences in various cognitive and psychological characteristics between the attempters and the non-attempters.

First, the K-BDI-2 scores of the attempters and the non-attempters were significantly higher compared to HCs. This result supports previous research findings indicating a close relationship between depressive symptoms and suicide risk [29]. However, while differences were observed between the depressive patient group and the HCs, there was no significant difference between the attempters and the non-attempters, necessitating further discussion. Second, both the attempters and the non-attempters exhibited significantly lower scores on the K-RFL total score compared to the HCs. Specifically, within the K-RFL factors, the depression patient group scored significantly lower on the survival and coping beliefs, family responsibility and child-related concerns and future expectations scales compared to the HCs. This suggests that one of the protective factors against suicide in the depressive patient group is lacking optimism, and lower expectations for the future have a significant impact on suicide. And the fear of death and social disapproval scores did not show significant differences between the three groups, suggesting that both the HCs and patients with depression share similar levels of fear regarding death and social disapproval. However, similar to the BDI-2 results, there was no significant difference between the attempters and the non-attempters, which may be attributed to the commonality of depression in both groups [30]. The results of the K-BDI-2 are consistent with previous studies, which have found no significant difference in depressive symptoms between individuals with a history of suicide attempts and those without. Among patients already diagnosed with depressive disorders, the difference in depressive symptoms based on the history of suicide attempts is minimal [31]. Furthermore, the meaning and quality of the RFL for an individual may be more important than simply the score difference and given that depression has a negative correlation with RFL [32], it can be inferred that both the K-BDI-2 and K-RFL are more influenced by current psychological distress, hopelessness, and suicidal ideation rather than a mere history of suicide attempts.

Third, there were no significant differences in the language comprehension (VCI) of the K-WAIS-IV among the three groups, indicating that all three groups fell within the average range and that basic knowledge and vocabulary issues are generally less affected by psychological factors or maladaptation [33]. Therefore, language comprehension was confirmed to be a stable indicator regardless of psychopathology, consistent with previous K-WAIS-IV related studies.

The PRI and PSI scores of both suicide attempters and non-attempters were significantly lower than those of HCs. This suggests that while MDD has an overall impact on cognitive function, the presence or absence of a suicide attempt itself does not influence differences in individual cognitive functions.

Similarly, the FSIQ was significantly lower in both suicide attempters and non-attempters compared to HCs. Statistically, while no significant differences were observed for each individual measure, small differences may accumulate and manifest as a significant difference in FSIQ. This also provides an important implication that depression and suicide attempts may have a greater impact on overall cognitive integration abilities. This highlights the need to consider improvements not only in individual cognitive functions but also in the overall cognitive integration abilities in therapeutic approaches. However, no significant difference was observed between suicide attempters and non-attempters. MDD itself affects overall cognitive function, which is commonly observed regardless of whether a suicide attempt has occurred. The cognitive decline observed in individuals with MDD may contribute to overall lower cognitive performance, which could explain the lack of differences between attempters and non-attempters [34].

Lastly, when comparing MMPI-2 scales between groups, there were no significant differences in the validity scale, contrary to previous studies suggesting that attempters report more psychological problems and seek help more frequently than non-attempters [35]. In the restructured clinical scales, the RC9 scales showed significant differences between the attempters and the non-attempters. This suggests a tendency for the attempters to exhibit externalizing symptoms compared to the non-attempters, possibly indicating poor impulse control or a heightened sense of self. In the content scale, the ANG scale and ASP scale were significantly higher in the attempters compared to the non-attempters. Specifically, significant differences were observed in the sub-scales of ANG such as explosive behavior (ANG 1) and irritability (ANG 2). Considering the high face validity of the content scale, attempters may exhibit patterns of anger, hostility, violent behavior, impulsivity, substance abuse, and antisocial behavior, indicating aggressive behavior towards the examiner. These results suggest that attempters may experience anger more intensely than others and have difficulty controlling it appropriately, which can lead to externalized psychological issues such as impulsivity, aggression, and interpersonal conflict [36]. In the supplementary scale, the Re was significantly lower in the attempters compared to the non-attempters, while the MAC-R were significantly higher. This indicates that attempters may have a reduced sense of social responsibility and a higher propensity for substance-related problems, suggesting a higher likelihood of impulsivity related to substance use [37]. The close relationship between impulsivity and substance use has been consistently reported, but since many studies have been limited to impulse control disorders and substance use disorders, there is a need for more research on impulsivity and substance use as characteristics of the attempters. In the PSY-5 scales, the DISC scale was significantly higher in the attempters compared to the non-attempters. In the content scales, the ANG scale was also elevated in the attempters. This indicates that the attempters experience psychological vulnerability in externalizing psychological issues, such as impulsivity, poor behavioral control, and anger. The DISC scale corresponds to significant increases in RC9, reflecting tendencies toward impulsivity and dysregulated behavior, while the ANG scale reflects heightened anger expression.

The findings of this study provide several clinical implications. The results indicate that individuals with a history of suicide attempts had lower perceptual reasoning and processing speed scores compared to HCs. However, these differences were not unique to suicide attempters, as similar patterns were observed in non-attempters with MDD, suggesting that cognitive difficulties are more strongly associated with MDD itself rather than suicide attempt history. Moreover, suicide attempters exhibited higher impulsivity, anger, and disconstraint, as indicated by MMPI-2 scores. These findings suggest that suicide prevention efforts should focus more on emotional regulation and impulse control interventions rather than cognitive training. Additionally, both suicide attempters and non-attempters scored significantly lower on the K-RFL scale compared to HCs, with notably lower scores in the future expectation subscale. While hopelessness did not significantly differ between the two clinical groups, it is strongly associated with suicidal ideation. Therefore, interventions addressing both hopelessness and suicidal thoughts should be included in suicide prevention strategies.

Overall, these findings emphasize the need for suicide prevention strategies that target impulsivity, anger, and hopelessness rather than focusing primarily on cognitive training. Future research should explore individualized interventions that address both emotional dysregulation and hopelessness in young adults with MDD.

Limitations of this study include the relatively small sample size and the fact that data were obtained from a single psychiatric department, potentially limiting the generalizability of the findings. Furthermore, as the study was restricted to young adults in their 20s, future research should aim to expand the sample to encompass a broader age range and more diverse psychiatric conditions for more comprehensive insights. The K-BDI-2 and K-RFL, as self-report instruments, are susceptible to response biases and defensive attitudes. Incorporating clinician-rated tools such as the Hamilton Depression Rating Scale could improve the objectivity and accuracy of assessments. Another key limitation of this study lies in the categorization of all suicide attempters into a single group, despite their considerable heterogeneity. Important clinical characteristics-such as suicide intent, the number and severity of past attempts, and family history of suicide-were not incorporated into the group classification. As a result, meaningful within-group differences may have been masked, leading to an overly simplified comparison structure. Furthermore, the relatively small sample size limited the statistical power to detect subtle group differences and precluded the use of covariate-adjusted models (e.g., ANCOVA, regression). Although we reported comorbidity profiles in detail and observed notable differences between groups (e.g., comorbidity rate: 57.2% in attempters vs. 33.3% in non-attempters), these variables were not statistically controlled in the main analyses due to sample size constraints. This may have influenced the relatively limited number of significant differences found between clinical groups.

It is also important to note that the dataset was derived from real-world clinical assessments not originally designed for research purposes, which inevitably introduced structural limitations in terms of sample balance, covariate availability, and analytic flexibility. To ensure consistency and avoid bias due to missing data, we included only participants with complete records on all psychological assessments (BDI-2, RFL, WAIS-IV, MMPI-2) and clearly documented suicide attempt histories. While this strict inclusion strategy helped enhance internal validity, it led to a reduced sample size and limited generalizability. Moreover, the retrospective nature of the study introduces variability in the timing of psychological assessments relative to clinical events such as suicide attempts. Some participants may have completed assessments shortly after an attempt, while others may have done so months later. These temporal inconsistencies limit comparability and may have influenced the measured psychological states. Finally, given the cross-sectional and retrospective design, the study cannot determine causality between psychological variables and suicidal behavior. Future research should adopt prospective, longitudinal designs with sufficient sample sizes and standardized protocols to enable refined groupings, covariate adjustment, and temporal precision in identifying risk factors.

In conclusion, the findings of this study provide clinical insights into the cognitive and psychological characteristics of young adults with MDD and a history of suicide attempts. The results suggest that suicide attempters exhibit higher impulsivity and difficulties in impulse control, emphasizing the need for targeted interventions focusing on emotional regulation. Future research should address the limitations of this study by employing longitudinal designs and larger, more diverse samples to better understand the underlying mechanisms of suicide risk in young adults with depression.