The "High Holiday" became popular after a story from High Times in 1991.
The study analyzed data on fatal auto crashes in the United States over a 25-year period.
The study compared the number of driver deaths April 20, with the number of driver deaths on April 13 and April 27, during the study period. They compared this with the number of drivers involved in fatal vehicle crashes on April 13 and April 27 (which are a week before and a week after April 20).
John Staples, a professor of medicine at the University of British Columbia, and Donald Redelmeier, of the University of Toronto, compared the number of drivers involved in deadly crashes from 4:20 p.m.to midnight that day - long celebrated by stoner culture - to the same time span on a day a week earlier and a day a week later.
The risk is even higher among young drivers, they found - for drivers 21 or younger, the increased risk grew to 38 percent.
And geographic analysis suggested that the absolute risk increases were greatest in NY state (74% increase), Texas (28% increase), and Georgia. The celebrations often feature synchronized mass consumption of cannabis at exactly 4:20 p.m.
When Canada legalizes recreational marijuana use this summer, nearly 100 million people in North America will live in a place where it is legal to consume cannabis, Staples said.
He's hoping the results of the paper, which was published Tuesday in JAMA Internal Medicine, can bring awareness to the issue - and ultimately prevent more injuries. "It is possible that some states with high base-rates of cannabis consumption exhibit little increase in consumption on 4/20". In addition, the study includes data for the last 25 years, and so it includes a period of time well before recreational marijuana became legal.
But it's hard to know how closely the two are linked because USA federal prohibition on marijuana limits the types of research that can be done on it, Staples said.
The day, an unofficial holiday for marijuana legalisation supporters, is associated with an increased risk of vehicle accidents comparable to that seen on Super Bowl Sunday: American football's championship final.
The 2017 Canadian Cannabis Survey found that only half of the pot users thought that cannabis use impacted driving.
The researchers said that policymakers may want to consider these risks in places where marijuana is legal, and pay particular attention to strategies to curtail driving under the influence or marijuana.
'It's a really relevant question to be thinking about now since legalization seems to be progressing across the United States and in Canada, ' Staples said.
The researchers didn't know how many drivers drive while high.
Previous studies have found that other events are linked with an increase in driving fatalities. In the interim, clinicians in trauma centers might consider extra staffing, and clinicians in ambulatory care offices might warn patients to avoid unnecessary night driving on Super Bowl Sunday.
"My message to the public is: Don't drive high", Staples told VICE.
Marijuana users' self-proclaimed holiday is linked with a slight increase in fatal US auto crashes, an analysis of 25 years of data found.
The researchers hope that their results encourage authorities to advocate for safer travel options on 4/20, such as public transit, rideshares, taxis and designated drivers. The investigators also note that cannabis retailers and 4/20 event organizers have an opportunity to serve their customers and save lives by warning users not to drive while high.
"We just don't have enough data to know if ME has worse problem than anywhere else in the country", said University of British Columbia researcher John Staples. "Thoughtful policies can eliminate drugged driving and keep our roads safe", he said.