One of the leading contributors to illness burden in young people is major depression disorder (MDD) (Mokdad et al., 2016). Adolescent MDD is a prevalent mental illness with a high-lifetime prevalence and poor prognosis (Avenevoli et al., 2015). Depression is becoming increasingly common among adolescents, with an annual increment in prevalence rates from 8.7 % in 2005 to 11.3 % in 2014 (Mojtabai et al., 2016). Depression is associated with difficulties in both social functioning and academic performance, as well as a higher risk of smoking, drug abuse, and suicide, in adolescent patients (Hauenstein, 2003). Effective treatment is critical due to the severity of this disorder. The Treatment of Adolescents with Depression Study (TADS) found that the remission rates in the 12-week acute treatment phase for adolescent MDD was 37 % with antidepressant medication combined with cognitive behavioral therapy (CBT) and only 23 % with single antidepressant treatment, compared with 17 % for the placebo group (Kennard et al., 2006). Moreover, antidepressants have several common side effects, including headaches, gastrointestinal discomfort, and altered sleep rhythms, with the greatest concern being the risk of suicide (Miller and Campo, 2021). The treatment efficacy of antidepressants varies significantly among individuals, and factors that account for this variation in the treatment response remain poorly understood. Moreover, it normally takes at least 6–8 weeks to determine whether the patient is benefiting from the treatment. Patient response to treatment can be predicted in advance using specific factors, which can then be used to guide the best dosing regimen and improve the risk-benefit ratio. It has been reported that socio-demographic factors, clinical characteristics, comorbid disorders, neuroimaging indices, and genetic measures as well as psychosocial factors have all been proposed as potential predictors of treatment response (Kemp et al., 2008).

Personality traits (PTs) are one of the valid predictors for antidepressant treatment outcomes among adult patients. It has been reported that scores on neuroticism, agreeableness, and openness can potentially predict response to antidepressant treatment (Bagby et al., 2008; Du et al., 2002; Naito et al., 2022). However, most current studies have only focused on adults with depression. There is evidence suggesting similarities in the clinical symptoms and rates of psychiatric comorbidity between adolescent and adult patients with depression (Kovacs, 1996). However, the response to antidepressant treatment has been reported to be different in depressed patients of different ages (Kaufman et al., 2001; Mulder et al., 2003). Furthermore, there were remarkable differences in the efficacy of antidepressants versus placebo between depressed adults and adolescents (Cipriani et al., 2018; Cipriani et al., 2016).

PTs have been associated with elevate risk of developing depressive symptoms in Chinese adolescents (Gong et al., 2020). However, the relationship between PTs and antidepressant efficacy in adolescents remains elusive. The increasing prevalence and poor treatment response of depression in adolescents, as well as the lack of research on PTs in this population, led us to conduct an open-label, flexible-dose, 8-week study to investigate the association between depression and PTs in adolescents and whether PTs can influence the antidepressant response.