For example, while a systematic review and meta-analysis on the efficacy of PGx tests for CYP2D6 and CYP2C19 in depressive disorders in adults showed that PGx for treating depression was more useful than treatment as usual (TAU) [12] and improved remission of depressive symptoms [13], it is not known whether these findings would also be mirrored in the paediatric population. This evidence concerns the gene CYP2C19 and major depressive disorder.