New study finds worrisome statistics around medical cannabis users operating vehicles

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More than half of people who take medical cannabis for chronic pain say they've driven under the influence of cannabis within two hours of using it, at least once in the last six months, according to a new study.

One in five of them said they'd driven while 'very high' in the past six months, researchers from the University of Michigan Addiction Center report in the journal Drug & Alcohol Dependence .

Lead author Erin E. Bonar, Ph.D., assistant professor of psychiatry and a practicing at the U-M Addiction Treatment Services finds the results of a survey of 790 Michigan medical cannabis users troubling.

Hundreds of thousands of Americans have state approval to use , including nearly 270,000 in the state of Michigan, according to Statista, as of May 2018. Michigan is second only to California for the highest number of medical marijuana patients in a state.

Risky driving

Bonar says that when people drive under the influence of marijuana their and coordination may be slowed down and they could have a harder time reacting to the unexpected. If they are in a risky situation, they could be more likely to be involved in motor vehicle crash, because they would not be able to respond as quickly.

For the study, the team surveyed adults in Michigan who were seeking recertification or a new certification for in 2014 and 2015. The researchers asked about respondents' driving habits for the past six months.

Fifty-six percent of participants reported driving within two hours of using cannabis, 51 percent reported they drove while a "little high", and 21 percent reported driving while "very high."

"There is a low perceived risk about driving after using marijuana, but we want people to know that they should ideally wait several hours to operate a vehicle after using cannabis, regardless of whether it is for medical use or not," Bonar said. "The safest strategy is to not drive at all on the day you used marijuana."

There is uncertainty about how marijuana could affect driving for chronic daily users, who might have even longer-lasting effects that linger in their system, Bonar added.

Uncharted territory

To add complexity to the issue, in November Michigan voters approved the use of recreational marijuana in the state. In early December, it became legal under state law for any Michigan resident over the age of 21 to use marijuana inside a private residence, and to grow up to 12 plants for personal use. Retail sales are only allowed for those with medical marijuana cards issued by the state. Marijuana use and possession remains illegal under federal law.

In light of this policy change, Bonar says, all cannabis users need a clear understanding of the side effects of this drug.

"When it comes to driving, we haven't yet figured out the best way to know how impaired marijuana users are at any given time," she says. "With alcohol, you can do some quick math based on the amount you drank, and take an educated guess at your blood alcohol level. For marijuana, an estimate like this would be complicated. It's hard to quantify because there is a lot of variation in marijuana dosing, THC potency, and route of administration. We also don't have specific guidelines yet about when exactly it would be safe to operate a vehicle."

Bonar says the goal of her team's study—conducted before the passage of the ballot question that resulted in the change in state law—is to help medical marijuana users to be safer on the roads.

"We believe more research is needed to inform a larger public education effort that will help individuals understand the risks for themselves, and others, of driving while under the influence of cannabis," she says. "It is especially needed during this time of rapid policy change as many states are determining how to manage marijuana legalization. We also need clearer guidelines about dosing and side effects with an understanding of how individual differences in things like sex and body weight interact as well."

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Citation: New study finds worrisome statistics around medical cannabis users operating vehicles (2019, January 9) retrieved 17 October 2019 from
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Jan 09, 2019
"refer madness".... no data on how many deaths or injuries are related to legalization of marijuana. And no hard numbers usually means low grade talk. Since it has been a recent change, not a lot of data is available, but at least several months data can be used to show the effect of legalization on driving, on different crimes, on local suicide, etc.

Jan 09, 2019
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Jan 11, 2019
'reaction time' is a distant pale second to attention and lack of experience (of driving while medicated). The real hazard is forgetting what you are doing and how important and dangerous driving is, aka getting distracted. If you are on task, aka mindful, you have good chance of drive with adequate safety no matter how impaired. It is impaired judgment, not faculties, that is dominant risk. Judgement seems to be more impaired by alcohol than THC. THC tends to possibly even increase concern, or tendency to compensate for intoxication, where alcohol can create overconfidence or lack of concern. But ultimately being aware of your capabilities, which can vary from person to person, in any condition is the determining factor, not some near-mindless metric 'reaction time'. The common reference to that metric is tiresome, as is the concept that it is a substitute for judgement...the misguided pushing for driverless vehicles than can 'react' but have no contextual judgement whatsoever.

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