Both tramadol and codeine are CYP2D6 substrates. A recent study has shown that people who are ultrarapid and poor CYP2D6 metabolizers are less liekly normal or indeterminate metabolizers (p = 0.01). After adjusting the CYP2D6 activity score for drug–drug interactions, uncontrolled pain was reported more frequently for people with reduced CYP2D6 activity (odds ratio: 0.50; 95% CI: 0.25–0.94). This finding, reported in the journal Pharmacogenomics, suggests that genomic screening could be very useful as a tool in selecting effective analgesia on an individualised basis.