Antidepressant medication influences cellular lipogenesis, being associated with metabolic side effects including weight gain. Due to the increasing use of antidepressants in children and adolescents, their metabolic and endocrine adverse effects are of particular concern, especially within this pediatric population that appears to be at greater risk. Genetic factors with a possible influence on antidepressant's adverse effects include CYP [cytochrome P450 (CYP450)] polymorphisms. We target to evaluate the efficacy of the pharmacogenetic testing, when prescribing antidepressants, in correlation with the occurrence of adverse events and weight gain. Our research was performed between the years 2010 and 2016, in the University Clinic of Child and Adolescent Psychiatry, Timisoara, Romania. We recruited 80 patients, children and adolescents with depressive disorders. Our study sample was divided in two groups: G1 - 40 patients took treatment after pharmacogenetic testing, and G2 - 40 patients without pharmacogenetic testing before the treatment election. Our results show statistically significant differences concerning the weight gain for groups G1 (with pharmacogenetic testing) and G2 (without pharmacogenetic testing). The CYP genotype and the pharmacogenetic testing, for choosing the personalized antidepressant therapy in children and adolescents with depressive disorders, proved to be good predictors for the response to antidepressants and the side effects registered, especially for weight gain. The significant correlations between the CYP polymorphisms for group G2 (without pharmacogenetic testing) and the weight gain/body mass index (BMI) increase, as major side effects induced by antidepressants, proved the fact that the pharmacogenetic screening is needed in the future clinical practice, allowing for individualized, tailored treatment, especially for at-risk pediatric categories.