Cannabis consumption associated with the April 20 counterculture “holiday” known as 4/20 has been linked with a 12% increase in fatal traffic accidents, according to research published in JAMA Internal Medicine.

The “holiday” — in which marijuana activists and enthusiasts gather to consume cannabis at 4:20 PM on April 20 — was popularized after being featured in the publication High Times.

Researchers from St. Paul’s Hospital in Vancouver, British Columbia, examined publically available statistical data obtained from the US National Highway Traffic Safety Administration’s Fatality Analysis Reporting System to determine the relationship between fatal traffic crashes and 4/20 participation.

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Twenty-five consecutive years of data were examined, from January 1992 through December 2016. Primary analysis evaluated the relationship between number of drivers involved in fatal traffic crashes between 4:20 PM and 11:59 PM on April 20 and fatal crashes during the same time interval 1 week earlier and later. Prespecified stratified analyses examined individual and geographic variations.

During the study period, 1.3 million drivers were involved in 882,483 crashes with 978,328 fatalities. On April 20, a total of 1369 drivers were involved in fatal crashes during between 4:20 PM and 11:59 PM; 2453 drivers were involved in fatal crashes during the same time interval on control days (7.1 and 6.4 fatalities per hour, respectively). Overall, the risk for being involved in a fatal crash was “significantly higher” on April 20 (relative risk: 1.12; 95% CI, 1.05-1.19; P =.001).

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Subgroup analysis indicated that younger drivers experienced an increase in relative risk, while geographic analysis suggested that absolute risk increases were highest in New York, Texas, and Georgia (excess of 36, 32, and 29, respectively). No change in fatal crashes was indicated before 4:20 PM or on nearby dates.

“Although the vast majority of Americans do not celebrate 4/20, the observed association was comparable in magnitude to the increase in traffic risks observed on Super Bowl Sunday,” the researchers concluded. “Policy makers may wish to consider these risks when liberalizing marijuana laws.”


Staples JA, Redelmeier DA. The April 20 cannabis celebration and fatal traffic crashes in the United States [published online February 12, 2018]. JAMA Intern Med. doi:10.1001/jamainternmed.2017.8298