There is a documented spike in fatal car crashes that take place across the United States on April 20, a day commonly known among marijuana users as a ‘weed holiday.’

A new study published by scientists at the University of British Columbia found that over a period of 25 years, fatal crashes constantly jump up on the day of the marijuana celebration. Researchers found a 12 percent increase on that particular day, according to Reuters.

Dr. John Staples, who authored the paper and led the study, said the results were alarming because even though “twelve percent may not sound like much,” he said not many Americans smoke weed, which means the rise is more significant.

Motivation behind the research

Staples said he was motivated to do the research because as a clinical assistant professor working at a hospital, he reported expecting a surge of visitors on the date annually as a result of a nearby festival where marijuana is regularly consumed, according to ABC News.

The study did not confirm whether drivers who were involved in crashes were more likely to use marijuana or not. However, Staples said weed smokers and those who consume edibles were the most likely cause of the increase, according to Reuters, adding that marijuana users should learn not to drive while under the influence of the drug.

The study looked at 25 years of information from the U.S. National Highway Traffic Safety Administration, from 1992 to 2017, to calculate numbers and whether spikes occurred on the holiday, according to ABC News.

Harm reduction a major priority

Jolene Forman, who works with the Drug Policy Alliance, an organization that advocates for harm reduction in drug policies, said other factors could be playing a role in the rise, according to Reuters. Forman pointed out that white nationalists also declare the day a holiday, as it was the day of Adolf Hitler’s birthday.

An estimated 55 million Americans are believed to use marijuana on anything resembling a regular base, including those shopping at a Las Vegas dispensary. While another 78 million have smoked it in the past, but no longer do. It’s almost as common as cigarette smoking, according to a survey from Marist Poll published in April 2017.

Younger drivers are particularly at risk, according to Staples. The study found that when broken down into age groups, drivers under 21 were 38 percent more likely to be involved in a car crash that day.