Sober up: Time from last drink to a road traffic injury.

PURPOSE: There is no intervention that quickly reduces a person's blood alcohol content (BAC). "Sober up before you drive" may prevent road traffic injury (RTI) caused by alcohol consumption. The aim of this study was to analyze the risk of RTI on an hourly basis (1-6 hours) after the last drink and the determinants of this risk.

METHODS: This was a case-crossover study of alcohol consumption among 430 patients who suffered a RTI and arrived at an emergency department in a large hospital in Mexico City from January to April 2022.

RESULTS: Of the 430 patients studied, 46 reported drinking within one hour before the RTI, for a risk ratio (RR) of 7.7 (95% CI [5.6, 10.4]). This RR decreased to 2.2 (95% CI [1.3, 3.7]) for the 12 patients drinking in the second hour before the RTI and was null for those drinking earlier (p ≤ 0.001 for the trend). The induction time was 3 hours among those with higher BAC and intoxication levels. The RR for a RTI decreases 71% from the first to second hour from the last drink and 32% from the second to third hour. This decrease was similar among those intoxicated and those with increased BAC. In multiple regression models, higher levels of intoxication and higher BAC remained associated with higher RRs.

DISCUSSION: People should avoid driving after drinking. Waiting to drive, walking, or riding after drinking reduces the risk of a RTI, especially for people with higher BAC and intoxication levels.