Introduction

Drug overdose deaths are at historic levels; over 106 000 drug overdose deaths occurred in 2021 compared with just under 68 000 in 2018.1 Changes in the illegal drug supply, such as the rise in synthetic opioids other than methadone, including fentanyl and fentanyl analogues (hereafter, ‘synthetic opioids’) beginning in 2013, have contributed to increasing overdose mortality rates in recent years.2 3 Since 2020, overdose-related morbidity and mortality have been exacerbated by the COVID-19 pandemic.4–6 For every fatal drug overdose, it is estimated that there are many more non-fatal drug overdoses. For example, in 2018, data from emergency departments (EDs) estimated 897 523 non-fatal drug-involved overdose ED visits in the USA,7 while mortality data from the same year identified 67 367 drug overdose deaths.8 However, despite having data sources such as these available to estimate the ratio of fatal to non-fatal overdoses, minimal information exists on long-term national trends and how this metric might differ by drug type. Information on the ratio of fatal to non-fatal overdoses can be used to understand the lethality of different drug types, estimate overdose burden in areas with only one data source or where one data source is delayed (eg, mortality data), and project the number of fatal overdoses when the number of non-fatal overdoses is known since fatal data are typically much more delayed. This metric can also inform response and prevention efforts by identifying drugs more likely to be involved in fatal overdoses so that harm reduction services (eg, naloxone and fentanyl test strip distribution), linkage to care and treatment (eg, medications for opioid use disorder), behavioural health services and communications campaigns can be deployed. This study seeks to assess trends in fatal and non-fatal overdose counts and to estimate the ratio of fatal to non-fatal overdoses treated in EDs for all drug, all opioid-involved, synthetic opioid-involved, heroin-involved, stimulant-involved, and opioid- and stimulant-involved polysubstance overdoses, from 2010 to 2020 in the USA.

MethodsFatal overdose data

To estimate the number of fatal overdoses, the Centers for Disease Control and Prevention’s National Vital Statistics System (NVSS) Multiple Cause of Death Data from 2010 to 2020 were used.9 The NVSS mortality data are based on cause of death classification obtained from death certificates collected by state registries. The underlying cause of death field was queried for International Classification of Diseases, 10th Revision (ICD-10) codes indicating a drug overdose; these included codes X40–44 (unintentional), X60–64 (suicide), X85 (homicide) and Y10–14 (undetermined intent). If the record met the criteria for an all-drug overdose using the underlying cause of death field, the multiple cause of death field was queried for codes specifying the drug(s) involved in the overdose. Drug categories were defined as follows: all opioids (codes T40.0–T40.4, T40.6), synthetic opioids other than methadone (‘synthetic opioids’; T40.4), heroin (T40.1) and stimulants (T40.5, T43.6); deaths that had an overdose code for at least one opioid and one stimulant were considered opioid- and stimulant-involved polysubstance overdoses.

Non-fatal overdose data

To estimate the number of non-fatal overdoses treated in EDs (hereafter, ‘non-fatal overdoses’), data from the Healthcare Cost and Utilization Project (HCUP) Nationwide Emergency Department Sample (NEDS) database from 2010 to 2020 were used.10 NEDS provides estimates of the number of ED visits in the USA by using stratified random sampling of EDs from State Emergency Department and State Inpatient Databases; each record includes a sampling weight that can be applied to obtain a nationally representative estimate. NEDS data include information about ED visits and are not available at the patient-level; thus, it is possible persons who experienced multiple overdoses during the study period are captured more than once. All diagnosis and external cause of injury fields were queried for International Classification of Diseases, 9th or 10th Revision, Clinical Modification (ICD-9-CM or ICD-10-CM) poisoning codes indicating a drug overdose for six categories: all drug, all opioid-involved, synthetic opioid-involved, heroin-involved, stimulant-involved, and opioid- and stimulant-involved polysubstance (defined as at least one opioid and one stimulant poisoning code) overdoses (online supplemental box 1a).11 12 In October 2015, ICD-9-CM transitioned to ICD-10-CM; for this analysis, ICD-9-CM codes were used to query data from January (Quarter 1) 2010 through September (Quarter 3) 2015, and ICD-10-CM codes were used to query data from October (Quarter 4) 2015 through December (Quarter 4) 2020. Additionally, beginning in 2017, external cause of injury fields were included with other diagnoses and no longer retained in separate data elements. To minimise the impact of the ICD-9-CM to ICD-10-CM coding change that occurred during the study period (1 October 2015), all intents (unintentional, intentional self-harm, assault and undetermined) and encounters (initial, subsequent and sequela) were included. Visits that resulted in death were excluded. Records with missing data for discharge quarter were excluded from analysis (<0.5% of all drug overdoses per year).

Counts of fatal and weighted counts of non-fatal all drug, all opioid-, synthetic opioid-, heroin-, and stimulant-involved, as well as opioid- and stimulant-involved polysubstance overdoses, were calculated for each quarter during the study period; non-fatal synthetic opioid-involved overdose data were only available beginning in October 2015 when ICD-10-CM codes specific for this type of opioid overdose were implemented. Quarterly trends of non-fatal overdoses before and after the ICD-9-CM to ICD-10-CM code transition in October 2015 were assessed for discontinuity to determine appropriateness in combining these data for analysis.13 No substantial discontinuity in the number of non-fatal overdoses treated in EDs was found; thus, annual results for 2015 were deemed acceptable to present, with the acknowledgement of the coding change during the time period.13

Analytic plan

First, to assess trends, Joinpoint regression (V.4.9; National Cancer Institute) was used to calculate the average quarterly percent change (AQPC) in counts of fatal and non-fatal overdoses by drug type (ie, all drug, all opioid, synthetic opioid, heroin, stimulant, or opioid- and stimulant-involved polysubstance) from 2010 to 2020 (for non-fatal synthetic opioid-involved overdoses: from 2016 to 2020 only) and the quarterly percent change (QPC) for each segment where significant changes in trend (ie, Joinpoints) occurred. The permutation model selection method was used.14 For all fatal overdose drug types and all non-fatal overdose drug types except synthetic opioids, the maximum number of joinpoints allowed was five. For non-fatal synthetic opioid-involved overdoses, the maximum number of joinpoints allowed was three, as there were fewer data points assessed (ie, quarterly data from 2016 to 2020). A p value <0.05 was considered to be statistically significant. Second, the ratio of fatal to non-fatal overdoses was calculated by quarter and year from 2010 to 2020 for all drug, all opioid-involved, heroin-involved, stimulant-involved, and opioid and stimulant polysubstance overdoses; for synthetic opioid-involved overdoses, these were calculated from 2016 to 2020. Overdoses involving more than one type of drug are included in each applicable category (eg, an overdose involving co-use of opioids and stimulants would also be captured in the separate opioid-involved and stimulant-involved overdose categories). Similarly, these categories are not mutually exclusive (eg, all opioid overdoses include heroin overdoses). Figures of quarterly counts and the ratio of fatal to non-fatal overdoses over time were generated using the R ggplot2 package V.3.3.2.15 Quarters were defined as: Quarter 1 (Q1) 1 January–31 March; Quarter 2 (Q2) 1 April–30 June; Quarter 3 (Q3) 1 July–30 September and Quarter 4 (Q4) 1 October–31 December.

ResultsAll drug overdoses

During 2010–2020, there were a total of 628 277 fatal and 9 442 850 non-fatal all drug overdoses in the USA (table 1). The annual number of fatal all drug overdoses increased 140% from 38 329 in 2010 to 91 799 in 2020, and the annual number of non-fatal all drug overdoses increased 19% from 780 981 in 2010 to 926 326 in 2020 (table 1 and figure 1A). The AQPC was greater among fatal overdoses (2.0%; 95% CI: 1.3 to 2.7) compared with non-fatal overdoses, which did not have a significant change (0.3%; 95% CI: 0.0 to 0.7) (table 2). Fatal all drug overdoses had the greatest increase occur from Q3 2019 to Q2 2020 (QPC: 13.5%; 95% CI: 5.3 to 22.3) (table 2). Over the entire study period, the ratio of fatal to non-fatal all drug overdoses was 0.07 (~1 fatal:15 non-fatal); the annual ratio doubled during the study period, from 0.05 (~1 fatal:20 non-fatal) in 2010 to 0.10 (~1 fatal:10 non-fatal) in 2020 (table 1 and figure 1B).

Table 1

Annual counts of fatal overdoses and non-fatal overdose-involved emergency department visits and the ratio of fatal to non-fatal overdoses, by drug type, 2010‒2020*, USA

Figure 1

(A) Counts of fatal all drug overdoses and non-fatal all drug overdose emergency department visits and (B) ratio of fatal to non-fatal all drug overdoses, by quarter, 2010‒2020, USA. The vertical dashed line denotes where coding of non-fatal overdoses changed from ICD-9-CM to ICD-10-CM beginning 1 October 2015. ICD-9-CM, International Classification of Diseases, 9th Revision, Clinical Modification; ICD-10-CM, International Classification of Diseases, 10th Revision, Clinical Modification.

Table 2

Joinpoint regression analysis of trends* in counts of fatal overdoses and non-fatal overdose-related emergency department visits, by drug type, 2010‒2020†, USA

All opioid-involved overdoses

During 2010–2020, there were a total of 408 970 fatal and 2 419 835 non-fatal all opioid-involved overdoses in the USA (table 1). The annual number of fatal opioid-involved overdoses increased 225% from 21 089 in 2010 to 68 630 in 2020, and the annual number of non-fatal opioid-involved overdoses increased 121% from 133 501 in 2010 to 295 649 in 2020 (table 1 and figure 2A). The AQPC among fatal all opioid-involved overdoses was 2.8% (95% CI: 2.1 to 3.5) compared with 2.0% (95% CI: 1.3 to 2.8) among non-fatal overdoses (table 2). Fatal opioid-involved overdoses had the greatest increase occur from Q3 2019 to Q2 2020 (QPC: 16.3%; 95% CI: 7.1 to 26.4) (table 2). Over the entire study period, the ratio of fatal to non-fatal opioid-involved overdoses was 0.17 (~1 fatal:6 non-fatal); the annual ratio increased from 0.16 (~1 fatal:6 non-fatal) in 2010 to 0.23 (~1 fatal:4 non-fatal) in 2020 (table 1 and figure 2B).

Figure 2

(A) Counts of fatal opioid-involved overdoses and non-fatal opioid-involved overdose emergency department visits and (B) ratio of fatal to non-fatal opioid-involved overdoses, by quarter, 2010‒2020, USA. The vertical dashed line denotes where coding of non-fatal overdoses changed from ICD-9-CM to ICD-10-CM beginning 1 October 2015. ICD-9-CM, International Classification of Diseases, 9th Revision, Clinical Modification; ICD-10-CM, International Classification of Diseases, 10th Revision, Clinical Modification.

Synthetic opioid-involved overdoses

Fatal synthetic opioid-involved overdoses in the USA totalled 198 619 during 2010–2020; during 2016–2020 when data for both fatal and non-fatal synthetic opioid-involved overdoses were available, there were 172 089 fatal and 114 357 non-fatal overdoses (table 1). The annual number of fatal synthetic opioid-involved overdoses increased 1779% from 3007 in 2010 to 56 516 in 2020. From 2016 to 2020, the annual number of fatal synthetic opioid-involved overdoses increased 191% from 19 413 to 56 516, whereas non-fatal overdoses increased 91% from 17 610 to 33 670 (table 1 and figure 3A). In 2010, among fatal overdoses with any opioid involvement, 14% specifically indicated synthetic opioid-involvement; in 2020 this increased to 82%. In 2016, among non-fatal overdoses with any opioid involvement, 6% specifically indicated synthetic opioid-involvement compared with 11% in 2020. From 2010 to 2020, the AQPC among fatal synthetic opioid-involved overdoses was 7.1% (95% CI: 6.0 to 8.2); from 2016 to 2020 the AQPC among non-fatal synthetic opioid-involved overdoses was 4.2% (95% CI: 3.0 to 5.3) (table 2). Fatal synthetic opioid-involved overdoses had the greatest increase occur from Q3 2019 to Q2 2020 (QPC: 21.0%; 95% CI: 9.8 to 33.4) (table 2). During 2016–2020, the ratio of fatal to non-fatal synthetic opioid-involved overdoses was greater than 1, indicating that there were more fatal overdoses than non-fatal overdoses; the ratio increased from 1.10 (~1 fatal:1 non-fatal) in 2016 to 1.68 (~2 fatal:1 non-fatal) in 2020 (table 1 and figure 3B).

Figure 3

(A) Counts of fatal synthetic opioid-involved overdoses and non-fatal synthetic opioid-involved overdose emergency department visits and (B) ratio of fatal to non-fatal synthetic opioid-involved overdoses, by quarter, 2010‒2020, USA. The vertical dashed line denotes where coding of non-fatal overdoses changed from ICD-9-CM to ICD-10-CM beginning 1 October 2015. Prior to this coding change in October 2015, there were no diagnosis codes specific for synthetic opioids available for non-fatal data. ICD-9-CM, International Classification of Diseases, 9th Revision, Clinical Modification; ICD-10-CM, International Classification of Diseases, 10th Revision, Clinical Modification.

Heroin-involved overdoses

During 2010–2020, there were 118 309 fatal and 984 419 non-fatal heroin-involved overdoses in the USA (table 1). The annual number of fatal heroin-involved overdoses increased 334% from 3036 in 2010 to 13 165 in 2020, and the number of non-fatal heroin-involved overdoses increased 419% from 22 300 in 2010 to 115 720 in 2020 (table 1 and figure 4A). However, despite overall increases when comparing 2010 to 2020, heroin-involved overdoses began decreasing for both fatal and non-fatal overdoses beginning in Q3 and Q4 2016, respectively, and continuing through 2020 (table 2). The AQPC among fatal heroin-involved overdoses was 3.3% (95% CI: 2.7 to 3.8) compared with 4.3% (95% CI: 3.9 to 4.8) among non-fatal overdoses (table 2). Over the entire study period, the ratio of fatal to non-fatal heroin-involved overdoses was 0.12 (~1 fatal:8 non-fatal); the annual ratio of fatal to non-fatal heroin-involved overdoses decreased from 0.14 (~1 fatal:7 non-fatal) in 2010 to 0.11 (~1 fatal:9 non-fatal) in 2020 (table 1 and figure 4B).

Figure 4

(A) Counts of fatal heroin-involved overdoses and non-fatal heroin-involved overdose emergency department visits and (B) ratio of fatal to non-fatal heroin-involved overdoses, by quarter, 2010‒2020, USA. The vertical dashed line denotes where coding of non-fatal overdoses changed from ICD-9-CM to ICD-10-CM beginning 1 October 2015. ICD-9-CM, International Classification of Diseases, 9th Revision, Clinical Modification; ICD-10-CM, International Classification of Diseases, 10th Revision, Clinical Modification.

Stimulant-involved overdoses

During 2010–2020, there were 186 561 fatal and 740 736 non-fatal stimulant-involved overdoses in the USA (table 1). The annual number of fatal stimulant-involved overdoses increased 587% from 5914 in 2010 to 40 643 in 2020, and the number of non-fatal stimulant-involved overdoses increased 97% from 44 015 in 2010 to 86 898 in 2020 (table 1 and figure 5A). The AQPC among fatal stimulant-involved overdoses was 4.6% (95% CI: 3.9 to 5.4) compared with 2.0% (95% CI: 1.0 to 3.1) among non-fatal overdoses (table 2). Fatal stimulant-involved overdoses had the greatest increase occur from Q2 2019 to Q2 2020 (QPC: 11.5%; 95% CI: 6.4 to 17.0) (table 2). Over the entire study period, the ratio of fatal to non-fatal stimulant-involved overdoses was 0.25 (~1 fatal:4 non-fatal); the annual ratio of fatal to non-fatal stimulant-involved overdoses more than tripled, from 0.13 (~1 fatal:7 non-fatal) in 2010 to 0.47 (~1 fatal:2 non-fatal) in 2020 (table 1 and figure 5B).

Figure 5

(A) Counts of fatal stimulant-involved overdoses and non-fatal stimulant-involved overdose emergency department visits and (B) ratio of fatal to non-fatal stimulant-involved overdoses, by quarter, 2010‒2020, USA. The vertical dashed line denotes where coding of non-fatal overdoses changed from ICD-9-CM to ICD-10-CM beginning 1 October 2015. ICD-9-CM, International Classification of Diseases, 9th Revision, Clinical Modification; ICD-10-CM, International Classification of Diseases, 10th Revision, Clinical Modification.

Opioid- and stimulant-involved polysubstance overdoses

During 2010–2020, there were 112 887 fatal and 123 742 non-fatal opioid and stimulant polysubstance overdoses in the USA (table 1). The annual number of fatal opioid and stimulant polysubstance overdoses increased 951% from 2662 in 2010 to 27 966 in 2020, whereas non-fatal overdoses increased 193% from 5029 in 2010 to 14 753 in 2020 (table 1 and figure 6A). The AQPC among fatal opioid and stimulant polysubstance overdoses was 5.6% (95% CI: 4.7 to 6.5) compared with 3.0% (95% CI: 1.8 to 4.3) among non-fatal overdoses (table 2). Fatal opioid and stimulant polysubstance overdoses had the greatest increase occur from Q3 2019 to Q2 2020 (QPC: 18.4%; 95% CI: 8.4 to 29.3) (table 2). Over the entire study period, the ratio of fatal to non-fatal opioid and stimulant polysubstance overdoses was 0.91 (~1 fatal:1 non-fatal). The annual ratio increased from 0.53 (~1 fatal:2 non-fatal) in 2010 to 1.90 (~2 fatal:1 non-fatal) in 2020; counts of fatal opioid and stimulant polysubstance overdoses surpassed those of non-fatal overdoses beginning in 2018 (table 1 and figure 6B).

Figure 6

(A) Counts of fatal opioid- and stimulant-involved polysubstance overdoses and non-fatal opioid and stimulant polysubstance overdose emergency department visits and (B) ratio of fatal to non-fatal opioid- and stimulant-involved polysubstance overdoses, by quarter, 2010‒2020, USA. The vertical dashed line denotes where coding of non-fatal overdoses changed from ICD-9-CM to ICD-10-CM beginning 1 October 2015. ICD-9-CM, International Classification of Diseases, 9th Revision, Clinical Modification; ICD-10-CM, International Classification of Diseases, 10th Revision, Clinical Modification.

Discussion

In the USA, for every one fatal overdose, there were approximately 10 non-fatal overdoses in 2020, compared with approximately 1 fatal overdose per 20 non-fatal overdoses in 2010. The increase in the ratio of fatal to non-fatal all drug overdoses during the study period was primarily driven by increases in the number of fatal overdoses. Substantial increases in fatal all drug overdoses during this time period have been widely documented.16–18 Despite increased availability of harm reduction strategies in recent years (eg, naloxone distribution and education, fentanyl test strips),19–21 both fatal and non-fatal overdoses continued to rise through 2020.16 22 23 More extreme increases in fatal overdoses compared with non-fatal overdoses from 2010 to 2020 may be due to increases in overdoses involving more than one substance (intentionally or unintentionally) or more potent drugs (including the proliferation of synthetic opioids in the drug supply), which can increase the risk of fatal overdose,3 24–26 and increased and/or more comprehensive toxicology testing by medical examiners or coroners.

Among all opioid-involved overdoses, increases in the ratio of fatal to non-fatal overdoses were also primarily driven by increases in fatal overdoses, specifically, fatal synthetic opioid-involved overdoses. In 2010, for every one fatal opioid-involved overdose, there were approximately six non-fatal overdoses, compared with approximately one fatal per four non-fatal overdoses in 2020. Among synthetic opioid-involved overdoses, the number of fatal overdoses exceeded non-fatal overdoses, with the ratio increasing from 1.10 fatal per non-fatal in 2016 to 1.68 in 2020. Over the past decade, the rise of synthetic opioids, including highly potent illegally manufactured fentanyl and fentanyl analogues, has become a major public health concern and has contributed to increased overdose mortality.2 27 We found the proportion of fatal opioid-involved overdoses with a specific code indicating synthetic opioid involvement increased from 14% in 2010 to 82% in 2020, and the proportion among non-fatal overdoses increased from 6% in 2016 to 11% in 2020. These findings underscore the increasing risk of overdose mortality from synthetic opioid involvement.

In contrast to the other drug indicators assessed in this analysis, the ratio of fatal to non-fatal heroin-involved overdoses decreased from 2010 to 2020. This finding was due to non-fatal heroin-involved overdoses increasing more than fatal (419% and 334%, respectively). Despite the substantial increases in heroin-involved overdoses throughout the study period overall, decreases were observed in both fatal and non-fatal heroin-involved overdoses beginning in Q3 and Q4 2016, respectively, and continuing through 2020. This finding is corroborated by past research which identified a decrease in heroin overdose deaths from 2016 through 2020.16 The 2020 National Drug Threat Assessment reported that heroin availability remains high but has stabilised, corresponding with the decreases in heroin overdose mortality, and in some markets fentanyl is supplanting or surpassing heroin.28

In 2010, there was approximately one fatal stimulant-involved overdose per 10 non-fatal; this ratio increased substantially to nearly one fatal per two non-fatal overdoses in 2020. Again, the increase in the ratio of fatal to non-fatal stimulant-involved overdoses was driven by the large increase in fatal stimulant-involved overdoses during the study period. Stimulant-involved overdose increases in recent years have been primarily driven by methamphetamine and cocaine, both of which are readily available throughout the USA.28 Methamphetamine is highly potent and relatively inexpensive compared with other drugs.28 Additionally, there is no antidote for stimulant overdose like there is for opioid overdoses. A previous report found overdose deaths that involved cocaine and psychostimulants with abuse potential (such as methamphetamine) began increasing in 2012, and this continued through 2020.16

Opioid- and stimulant-involved polysubstance overdoses had the largest increase in the ratio of fatal to non-fatal overdoses during the study period, increasing from approximately one fatal per two non-fatal in 2010 to nearly two fatal per one non-fatal in 2020. From 2010 to 2020, increases in fatal opioid- and stimulant-involved polysubstance overdoses were substantially higher compared with non-fatal (951% and 193%, respectively), such that the number of fatal overdoses surpassed those of non-fatal overdoses beginning in 2018. Polysubstance overdoses involving both stimulants and other drugs, such as opioids (including fentanyl), are becoming more common; one study found that the rate of psychostimulant- and opioid-involved polysubstance overdose deaths surpassed those of psychostimulants alone in 2017.29

Limitations

This study and data sources used are subject to multiple limitations. First, the coding systems for identifying non-fatal overdoses in ED data changed from ICD-9-CM to ICD-10-CM on 1 October 2015. The newer ICD-10-CM codes are more specific and allow for capturing additional information on intentionality of the overdose (ie, unintentional, intentional self-harm, assault or undetermined intent) and encounter (ie, initial, subsequent or sequela). Because this analysis spanned the coding change, we included all intents and encounters in order to maintain consistency in comparison of trends; however, including all encounters could potentially capture ED visits that were not for an acute drug overdose. Second, changes in forensic toxicology testing vary over time (eg, increased testing and/or more comprehensive testing), which could contribute to increased identification of fatal overdoses, especially synthetic opioid overdoses. Third, the specificity in coding improved for both the fatal and non-fatal data, which may be reflected in the number of overdoses identified in both data sources. Among fatal overdoses, the percentage of records that identified the specific drug involved increased from 75% in 2010 to 94% in 2020.16 30 Among non-fatal overdoses, the coding transition from ICD-9-CM to ICD-10-CM and the introduction of more specific poisoning codes during the study period may have improved specificity.31 However, improvements in coding alone are unlikely to explain the substantial increases in fatal or non-fatal overdoses observed in this study.

Fourth, the non-fatal data only included overdoses that were treated in EDs; persons treated in the field without subsequent visits to an ED would not be recorded (eg, those treated and released by emergency medical service providers, which has been increasing in recent years).22 32 The percent of non-fatal opioid overdose EMS encounters that were not transported to a medical facility was 15.0% in 2018, 18.0% in 2020 and 22.0% in 2022, among EMS encounters in the National Emergency Medical Services Information System Nonfatal Opioid Overdose Surveillance Dashboard (which is not a nationally representative US sample).33 Thus, the number of non-fatal overdoses included in our analysis likely underestimates the true burden of non-fatal overdoses in the community; this would result in overestimation of the ratio of fatal to non-fatal overdoses. Future research could explore using other data sources to capture non-fatal overdoses with transport refusal or which were treated and released and estimate the ratio of fatal to non-fatal overdoses using additional data sources (eg, EMS data, HCUP NEDS and NVSS) to account for underestimation of non-fatal overdoses using HCUP NEDS data only. Fifth, the ED discharge data used to estimate the number of non-fatal overdoses come from billing/claims data, which are generated for insurance reimbursement purposes. These data (ie, the ICD-9-CM and ICD-10-CM billing codes) are not typically corroborated by toxicology testing to confirm the substance(s) involved in the overdose, which may result in misclassification of drugs involved in the overdose.34 Sixth, this study did not examine every drug type or common polysubstance drug combination, which could provide additional context to the changing overdose landscape. Lastly, data coinciding with the start of the COVID-19 pandemic were included in this analysis (Q2 2020–Q4 2020); care-seeking behaviour, including whether a person sought treatment in an ED following an overdose, may have had an impact on the number of non-fatal overdoses treated in EDs during this time period.5

Conclusion

Increases in the number of fatal and non-fatal overdoses were observed for all drug types assessed in this analysis, highlighting the worsening drug overdose epidemic. For all drug types except heroin, we found that large increases in fatal overdoses were the primary driver for the increase in the ratio of fatal to non-fatal overdoses, despite both fatal and non-fatal overdoses increasing during 2010–2020. This finding underscores a growing concern that overdoses are increasingly more likely to result in death, largely due to increased involvement of more than one substance and more potent drugs (including synthetic opioids, like illegally manufactured fentanyl) which can increase the risk of fatal overdose.3 24–26

An understanding of both the counts of fatal and non-fatal overdoses and the ratio of fatal to non-fatal overdoses can help to understand the lethality of different drug types, estimate overdose burden in areas with only one data source or where one data source is delayed (eg, mortality data) and inform response and prevention efforts such that they can be tailored to the individual and community. It continues to be imperative that harm reduction services (eg, naloxone and fentanyl test strip distribution), linkage to care and evidence-based substance use disorder treatment (eg, medications for opioid use disorder) and behavioural health services are effectively deployed in communities to help reduce overdose morbidity and mortality. Findings from this study can help to inform education programmes for first responders, healthcare providers, harm reduction organisations and community members about the heightened risk of experiencing fatal overdose among certain drugs.4