BACKGROUND: In 2023, the Office for National Statistics (ONS) attributed 46.8 % of fatal drug poisonings in England and Wales to opioids. However, this figure likely underrepresents the true scale of opioid-related deaths, as ONS cannot identify opioid involvement when ambiguous causes (e.g., multidrug toxicity) are used. This study used ONS and National Programme on Substance Use Mortality (NPSUM) data to provide a more comprehensive estimate of opioid-related deaths in England and Wales from 2011-2022.

METHODS: Deaths were identified as opioid-related by ONS and NPSUM where opioids were explicitly named as a cause. Further cases with ambiguous causes were identified by NPSUM as opioid-related by referring to the accompanying toxicology report.

FINDINGS: ONS has increasingly underestimated opioid-related deaths. In 2011, 574 heroin/morphine-related deaths were identified by ONS; while the estimated number was 813 (95 % CIs 765-866), reflecting a 29 % underestimate. By 2022, the underestimate had extended to 36 % (1264 deaths identified by ONS; estimated number 1980 [95 % CIs 1894-2074]). This correlates with increasing polypharmacy (median number of co-administered drugs: four in 2011, six in 2022, ρ=0.81). Similar trends were observed for other specific opioids for which ONS data were available: methadone, dihydrocodeine, codeine, tramadol, and fentanyl.

CONCLUSIONS: Increasing polydrug use in England and Wales is likely leading to the use of ambiguous drug-related causes of death instead of every drug being individually named, resulting in an underestimation of opioid-related deaths. This discrepancy has significant implications for funding, policy and public health initiatives aimed at addressing the UK's escalating opioid-related death crisis.