Approximately 25% of individuals may exhibit a lack of response to codeine or tramadol and/or toxicity due to variants in the CYP2D6 gene.34,35 Respiratory depression and fatalities have been reported in postoperative paediatric patients and other settings, linked to CYP2D6 ultra-rapid metaboliser status.36,37 Additionally, drug safety alerts from the Medicines and Healthcare products Regulatory Agency have highlighted an increased risk of Stevens–Johnson syndrome with carbamazepine, commonly prescribed for neuropathic pain, due to rare variants in HLA-A and HLA-B genes.38 This evidence concerns the gene CYP2D6 and respiratory depression.