We appreciate McCabe’s insightful comments regarding our recent article on alcohol and cannabis involvement in motor vehicle crash fatalities.1 He notes that, given the presence of up to three substances in the Fatality Analysis Reporting System (FARS), it would have been preferable to assess the presence of additional substances. The decision to focus on alcohol and cannabis was based on (1) alcohol and cannabis being the most prevalent substances involved in impaired driving and (2) the changing landscape of cannabis policy and increasing cannabis use in the United States.2,3 However, we agree that assessing coinvolvement of other substances is merited, and we included opioid involvement and other, nonopioid substance involvement in our main, fully adjusted model presented with our original article in supplemental Table A, an excerpt of which is provided here in Table 1.
TABLE 1—
Mixed Effects Multinomial Logistic Regression Models of the Odds of Alcohol Involvement by Blood Alcohol Concentration (BAC) Level, Fatality Analysis Reporting System: United States, 2000–2018
| Crash-Level Substance Involvement | Outcome, OR (95% CI)a | ||
| BAC 0.01%–0.049% | BAC 0.05%–0.079% | BAC ≥ 0.08% | |
| Cannabis involvement (vs no) | 1.56 (1.48, 1.65) | 1.62 (1.52, 1.72) | 1.46 (1.42, 1.50) |
| Opioid involvement (vs no) | 1.02 (0.95, 1.09) | 0.82 (0.76, 0.90) | 0.61 (0.59, 0.63) |
| Other substance involvement (vs no) | 1.42 (1.36, 1.48) | 1.42 (1.34, 1.50) | 1.02 (1.00, 1.04) |
Note. CI = confidence interval; OR = odds ratio.
aRef = 0.00%.
While McCabe is correct that these were not identified a priori as primary exposures, their relationship with alcohol coinvolvement can nevertheless be at least preliminarily ascertained through our models given that many of the same confounders would be applicable. Involvement of opioids was not associated with alcohol involvement at blood alcohol concentrations (BACs) lower than 0.05%, and was associated with decreased odds of alcohol involvement at BACs of at least 0.05%. We speculate this may be attributable to combined depressive effects of simultaneous opioid and alcohol use so that driving may be precluded in the first place.4 However, presence of a substance other than opioids and cannabis (e.g., stimulants, depressants, hallucinogens) was associated with increased odds of alcohol coinvolvement, especially at low BACs. Future research is needed to disentangle multiple substance‒impaired driving.
In addition, McCabe points out that there are several flaws with the cannabis testing data in FARS. We agree that cannabis testing can and should be improved in the future. From 2018 onward, FARS includes all involved substances, and the 2021 Infrastructure and Jobs Act includes funding for multiple substance‒impaired driving research and prevention, both of which should support future research on multiple substance‒impaired driving.5,6
ACKNOWLEDGMENTS
This study was supported by award R01AA026268 from the National Institute on Alcohol Abuse and Alcoholism (NIAAA).
Note. The content is solely the responsibility of the authors and does not necessarily represent the official views of NIAAA or National Institutes of Health. NIAAA had no role in the study design; collection, analysis, and interpretation of data; writing the report; and the decision to submit the report for publication.
CONFLICTS OF INTEREST
The authors have no conflicts of interest to report.
HUMAN PARTICIPANT PROTECTION
This study was determined to be not human participant research by the institutional review board at Boston University Medical Campus (protocol H-37378).
REFERENCES
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