By Pat Anson, PNN Editor

Has marijuana legalization made driving more dangerous?  There have been conflicting claims over the years that states where cannabis is legal have more car crashes. And one recent study found that over half of medical cannabis users drive while impaired.

A new study adds a little more clarity to the issue.

Researchers at Monash University in Australia looked at traffic fatalities in three U.S. states where recreational cannabis was legalized (Colorado, Washington and Oregon), and in eight neighboring states and British Columbia.

They found there was an average of one additional traffic fatality for every million residents. That may not sound like much, but when you consider there were 27 million people in the affected areas, it adds up to 170 additional deaths in the first six months after legalization.

Many of the additional deaths were attributed to “cannabis tourism” in which people in neighboring states and provinces purchased recreational cannabis in legalized states and then drove home while under the influence.

"The results suggest that legalizing the sale of cannabis for recreational use can lead to a temporary increase in traffic fatalities in legalizing states. This spills over into neighboring jurisdictions through cross-border sales, trafficking, or cannabis tourists driving back to their state of residence while impaired,” says lead author Tyler Lane, PhD, a postdoctoral research Fellow at Monash.

"Our findings suggest that policymakers should consult with neighboring jurisdictions when liberalizing cannabis policy to mitigate any deleterious effects."

Because the increase in fatalities was temporary, Lane believes it could be due to an initial “celebratory response to legalization” that contributes to cannabis tourism. His study was published in the journal Addiction.

Fatalities Drop in Medical Cannabis States

While fatalities rose in states with recreational cannabis, Lane notes that previous research has found a decrease in traffic fatalities in states that legalized medical marijuana. That may be because patients may be substituting cannabis for alcohol and other controlled substances used to relieve symptoms.

“There seem to be differences between medicinal and recreational user consumption patterns. Medicinal users have a tendency to substitute, but recreational users are more likely to treat alcohol and cannabis as complements and use them together,” Lane said in an email to PNN. 

“Because marijuana on its own is less impairing than alcohol, and combined used is much more impairing than either in isolation, it suggests that when people substitute alcohol for cannabis (in the medicinal use context), they will still be impaired, but to a much lower degree than if they were still using alcohol.” 

This “harm reduction role” of medical cannabis was noted in a 2016 Canadian study that found patients reduced their use of alcohol, illicit drugs and prescription drugs when cannabis was taken for medical reasons. 

Medical marijuana is currently legal in 33 states and Washington DC, and ten states allow its recreational use.