Cytochrome P450 2D6 (CYP2D6) is involved in metabolism of approximately 20% of commonly used drugs in varied fields such as psychiatry, oncology and cardiology. CYP2D6 is a highly polymorphic with single-nucleotide polymorphisms (SNPs), small insertions and deletions as well as larger structural variants including multiplications, deletions and hybridisations. The frequency of these variants changes across populations, while significantly affecting the drug-metabolizing enzymatic function of CYP2D6. Altered CYP2D6 function has been associated with both adverse drug reactions and reduced drug efficacy, and there is growing recognition of the clinical and economic burdens associated with suboptimal drug utilization in the patients.