Table 3.

Main findings reported by the studies included in the scoping review

Author(s), Year	Main findings regarding associations between drug seizures and drug mortality
Gladden et al., 2016	In 27 states examined:
	2013–2014 changes in fentanyl submissions were correlated (r=0.95) with changes in synthetic opioid-involved overdose deaths
Hall et al., 2021	In Ohio, 2009–2018:
	The authors’ “lethality index” ( based on counts of drug seizures and drug deaths) accounted for 93% of the variance in unintentional drug overdose deaths.
Jalal & Burke, 2020	In a model predicting US state-level 2017–2018 change in per capita drug overdose deaths based on 2017–2018 changes in per capita carfentanil, fentanyl, and heroin seizures:
	A significant positive association was observed only for carfentanil seizures.
Lowder et al., 2022	In the Washington/Baltimore High Intensity Drug Trafficking Area, in county-year models with measures of drug seizure cases overall, dosage units per capita for specific drugs, trafficking/money laundering organization disruptions, and socioeconomics, demographics, and opioid prescribing:
	The number of drug seizure cases was significantly and positively associated with next-year (2016–2020) drug overdose mortality rates, opioid-involved mortality rates, and fentanyl-involved mortality rates. Dosage units of cocaine seized per capita were also significantly positively associated with opioid- and fentanyl-involved mortality rates.
Mohler et al., 2021	In Indianapolis/Marion County, 2014–2018:
	Although fatal overdoses were spatiotemporally clustered around opioid drug seizures at distances/times examined (100, 250, 500, and 1,000 meters and 3, 7, 14, and 21 days), there was no significant difference pre- and post- seizure.
Ray et al., 2023	In Indianapolis/Marion County, 2020–2021:
	For all distances/times examined (100 meters/7 days, 250 meters/14 days,500 meters/21 days): Opioid-related seizures significantly associated with spatiotemporal clustering of drug overdose deaths, significantly higher post- than pre- seizure. Only for lowest distance/time examined (100 meters/7 days): stimulant-related seizures significantly associated with spatiotemporal clustering of drug overdose deaths, significantly higher post- than pre- seizure.
Rosenblum et al., 2020	In Ohio, 2010–2017, in models including various drug seizure measures, unemployment, poverty, income, opioid and suboxone prescribing, county and month fixed effects, and county-month linear trends:
	County-level seizures of fentanyl, carfentanil, and other fentanyl analogs were significantly and positively associated with overdose deaths overall. Significant association for fentanyl seizures was observed in medium and large counties; for carfentanil, in large counties only; for other fentanyl analogs, in small, medium, and large counties. Fentanyl seizures positively associated with overdose deaths most strongly in the same month, but also in the month prior and second month after; carfentanil seizures positively associated with overdose deaths in three months prior and in the same month, and to a lower extent in the month after; other fentanyl analog seizures negatively associated with overdose deaths two to three months prior, yet positively associated with overdose deaths in the same month and three following months. Direction and significance of results regarding seizures of other drugs (e.g., benzodiazepines) differed between analyses.
Slavova et al., 2017	In Kentucky, 2013–2016:
	Monthly numbers of fentanyl submissions were significantly and positively correlated with numbers of fentanyl-involved overdose deaths. No significant correlation observed between heroin submissions and heroin-involved deaths.
Sumner et al., 2022	In the US, 2014–2019:
	The Pearson correlation coefficient between heroin/synthetic opioid drug submissions and weekly opioid-involved overdose deaths was 0.61.
Tran et al., 2021	In Ohio, 2014–2018:
	The monthly number of seizures of fentanyl/analogs had a stronger correlation with overdose deaths than carfentanil seizures There was no statistically significant lag between fentanyl seizures and overdose deaths. Approximately 59% of the variance in overdose deaths in any given month was attributed to fentanyl seizures in that month. Numbers of smaller-weight drug seizures had a stronger association with overdose deaths than larger-weight seizures. The positive association between the number of fentanyl seizures (overall and by weight) and overdose deaths persisted in autoregressive models.
Zibbell et al., 2019	In Ohio, 2014–2017, in multivariate models including multiple drug seizure measures, opioid prescribing rates, linear and quadratic time trends, and single-lagged dependent variable:
	Fentanyl seizures and carfentanil seizures significantly and positively associated with opioid overdose deaths.
Zibbell et al., 2022	In Ohio, 2014–2019, in multivariate models including multiple drug seizure measures, linear time trends, and a single-lagged dependent variable:
	Seizures of cocaine with fentanyl were significantly positively associated with stimulant and cocaine overdose deaths. Seizures of methamphetamine with fentanyl were significantly and positively associated with methamphetamine overdose deaths. Seizures of methamphetamine without fentanyl were significantly and negatively associated with stimulant and cocaine overdose deaths. Seizures of fentanyl without methamphetamine or cocaine were significantly and positively associated with stimulant and cocaine overdose deaths.
Zibbell et al., 2023	In the US, 2014–2019, in multivariate models including multiple drug seizure measures and state and quarter fixed effects:
	Fentanyl/fentanyl-related compound seizure counts showed the strongest association with increases in opioid overdose death. Heroin seizure counts were also associated with increases in opioid overdose deaths. Methamphetamine and cocaine seizure counts were associated with decreases in opioid overdose deaths. When modeling proportions/percentages of seizures involving each drug, instead of counts of seizures, only the percentage of fentanyl/fentanyl-related seizures was significantly associated with increased opioid overdose deaths.
Zoorob, 2019	In the US, 2011–2017, in models with state and year fixed effects and population weights:
	Fentanyl/synthetic opioid seizure rate was positively and significantly associated with drug overdose mortality rates.