Fluoxetine ± Low-Dose Quetiapine in Adolescent Major Depression: Comparing Six-Week Effects on Depressive Symptoms and Body Composition—Pilot Study

Background: Data on early changes in body composition during acute-phase treatment in adolescents with major depressive disorder (MDD) remain limited. In particular, the utility of novel anthropometric indices reflecting central and visceral adiposity has not been explored in this population. This study therefore aimed to examine short-term clinical outcomes alongside detailed anthropometric measures in drug-naïve adolescent inpatients receiving fluoxetine-based pharmacotherapy. Methods: Prospective, clinician-directed, non-randomized inpatient study. Drug-naïve adolescents with severe MDD (n = 23) received fluoxetine 20 mg/day, with some patients additionally receiving low-dose quetiapine (100 mg/day) based on clinical indication for six weeks. Depressive symptomatology was evaluated by questionnaires Montgomery–Åsberg Depression Rating Scale (MADRS) and Children’s Depression Inventory (CDI). Conventional and novel anthropometric indices (BMI, WHtR; BRI, AVI, ABSI, BAI) were examined using the objective bioimpedance-derived method for body composition. Results: Depressive symptom severity decreased over the six-week treatment period, with significant improvements observed on both MADRS and CDI (time effect p < 0.001). Response and remission rates increased over time in the overall sample. No statistically significant changes were observed in conventional or novel anthropometric indices across the study period. Conclusions: In this prospective pilot cohort of adolescent inpatients with MDD, six weeks of fluoxetine-based pharmacotherapy was associated with improvement in depressive symptoms. No short-term changes were observed in anthropometric indices; however, given the small sample size and limited follow-up, these findings should be interpreted cautiously and cannot be considered definitive evidence of cardiometabolic safety.