It remains unclear whether marijuana affects a driver’s risk of crashing. But there is no doubt that marijuana impairs someone’s judgement and the skills needed to drive a car, according to a study released Thursday by the Governors Highway Safety Association.

As Massachusetts prepares for the opening of its first legal recreational marijuana stores, the national study provides some context for the challenges the state will deal with as more drugged drivers take to the road.

“Drugs can impair. Marijuana can impair,” said Jim Hedlund, the study’s author, who spent 22 years as a national highway traffic safety administrator.

“A lot of folks that use marijuana do not think that it can impair. In fact, they think they can drive better when they’re high,” Hedlund said. “That’s not the case.”

The message of “don’t drive drunk” has been pervasive in American culture for years. But that message is not necessarily getting out to people using drugs. 

The study found that in fatally injured drivers who were drug or alcohol tested between 2006 in 2016, the number of drunk drivers decreased while the number of drugged drivers grew. 

In 2006, among drivers killed in car crashes who were tested for drugs or alcohol, 7,750 drivers (41 percent) had alcohol in their system and 3,394 (27.8 percent) tested positive for drugs. In 2016, 5,743 of those drivers (37.9 percent) had alcohol in their system and 5,365 (43.6 percent) had taken drugs. 

The death data found that among drivers with drugs in their system, 41.1 percent had used marijuana. 

The report finds that both marijuana and opioids pose dangers to drivers. 

The report says studies are unclear about whether marijuana actually increases the risk of crashes. The best estimate is that using marijuana increases the risk of a crash by 25 percent to

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