A recently conducted study has found that U.S. drivers are 12 percent more likely to get into a fatal crash on April 20, even if they aren’t cannabis consumers. That date is the unofficial holiday devoted to celebrating marijuana. The researchers looked at data from the U.S. National Highway Traffic Safety Administration, specifically at 25 years’ worth of data collected in the agency’s Fatality Analysis Reporting System. The results of the study were published in the journal JAMA Internal Medicine.

Physicians John Staples of the University of British Columbia and Donald Redelmeier of the University of Toronto started with the year 1992 and ended with 2016. For the purpose of the study, a crash was considered fatal if one or more people died within 30 days of the collision. The increased risk amounted to 142 additional deaths over the 25-year period.

The researchers found that the risk of a fatal vehicle crash on American roads after 4:20 p.m. on April 20 is 12 percent higher than on similar days that have no particular connection to marijuana. For all of the April 20ths combined, there were 1,369 drivers involved in fatal motor vehicle crashes that occurred between 4:20 p.m. and 11:59 p.m. That worked out to 7.1 crashes per hour.

When compared to the days one week before and one week after April 20, the difference was large enough to be statistically significant. The identical 7-hour-and-40-minute period on April 13ths and April 27ths had 6.4 fatal crashes per hour. The researchers said that the number is “comparable in magnitude” to the increased risk seen on Super Bowl Sundays.

The younger the driver, the bigger the increase in risk. For drivers aged 21 years or less, the increased risk grew to 38 percent. For all age groups combined, men got into nearly three times as many crashes as women. However, the increase in risk on April 20 was about the same for both sexes.

All of these extra deaths occurred even though the vast majority of Americans do not celebrate the 4/20 holiday. The study does not consider whether the April 20 risk to a driver changes if they are in a state that has legalized cannabis. The research also does not consider whether cannabis played a direct role in the April 20 fatal crashes. Because cannabis lingers in the body for so long, a positive lab test does not mean the person was impaired.