According to a commentary, the CYP2D6 gene encodes cytochrome P450 2D6, an enzyme that plays a crucial role in the metabolism of all tricyclic antidepressants, most SSRIs, and about half of all antipsychotics. It notes that inter-individual variability in the function of this enzyme largely stems from polymorphisms, gene copy number variations and structural rearrangements that can change an individual's ability to metabolise CYP2D6 substrates, leading to categories of poor, intermediate, normal, and ultra-rapid metabolisers. However, as acknowledged, in the current study, CYP2D6 genotype was only able to account for half the variance in risperidone and aripiprazole metabolism. It suggests therefore that CYP2D6 testing results should be interpreted alongside other patient characteristics (such as age, renal function, and liver function) and concomitant medications before clinical implementation. It highlights that consideration of other medications is particularly important as there are many drugs that inhibit CYP2D6 and when present, can change an individual's genotype-predicted metaboliser status. It concludes that obtaining the greatest benefit from CYP2D6 genotyping requires integration with other clinical information routinely collected as part of good clinical practice.