For instance, while the Swiss treatment guideline for unipolar depression recommends the ABCB1 gene test for patients with inadequate or only partially responsive antidepressant treatment [39], testing for the CYP2D6 and CYP2C19 genotypes is not mentioned, despite the availability of international recommendation guidelines for PGx-guided selection and dosage adjustment of selective serotonin reuptake inhibitors and tricyclic antidepressants based on these genotypes [40,41]. Here, CYP2D6 is linked to major depressive disorder.