A number of states have moved to legalize marijuana and there’s growing evidence to suggest it’s behind an increase in crashes.

According to the Insurance Institute for Highway Safety (IIHS), crash rates spiked in California, Colorado, Nevada, Oregon and Washington following the legalization of recreational weed.

A study conducted by the group found that injury and fatal crash rates in all five states “jumped in the months following the relaxation of marijuana laws.” Compared to other Western states where recreational marijuana was illegal, the five states saw a six percent increase in injury crash rates and a four percent increase in fatal crash rates. However, the group noted only the increase in injury crash rates was statistically significant.

Also Read: GM May Need To Stop Testing For Weed To Attract More Employees

The findings are consistent with other studies, but the verdict is still out on whether or not marijuana alone makes drivers more likely to crash. In particular, the IIHS noted data collected from injured drivers at three emergency rooms in Denver, Portland and Sacramento showed “no increased crash risk associated with the drug, except when combined with alcohol.” However, the study did indicate that legalization might be encouraging more people to drink and use marijuana together.

There are other factors at play as marijuana legalization is usually accompanied by a “burst of enthusiasm,” that could see more people getting high and then getting behind the wheel. The IIHS also noted some states have even used marijuana legalization as part of their tourism promotions, so that could potentially lead to tourists driving high in unfamiliar areas. On the bright side, this enthusiasm usually tapers off as marijuana becomes more commonplace.

Studies have shown drugged drivers have slower reaction times, a harder time paying attention, more difficulty keeping their car centered in their lane, and make more mistakes when something goes wrong. However, they’re pretty chill otherwise as the IIHS noted they’re likely to drive slower, overtake less and keep a greater distance from the vehicle ahead of them.

IIHS-HLDI President David Harkey said, “Our latest research makes it clear that legalizing marijuana for recreational use does increase overall crash rates. That’s obviously something policymakers and safety professionals will need to address as more states move to liberalize their laws – even if the way marijuana affects crash risk for individual drivers remains uncertain.”

Recreational marijuana is legal in more than a third of U.S. states and that number is set to increase as Connecticut’s governor is expected to sign a recreational marijuana bill soon. Furthermore, studies have shown 68 percent of American adults favor legalization, while marijuana consumption has doubled between 2008 and 2019.