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Can you safely drive after smoking weed? 

January 18, 2016 by Steven M. Gursten

It isn’t legal in Michigan, plus one study finds ‘high’ drivers are twice as likely to crash

drive after smoking weed, image

As an automobile accident attorney, I keep getting asked two important questions about marijuana use and driving:

  • Can a person drive (legally) after smoking marijuana?
  • Is it safe to drive after smoking marijuana?

I decided to write the answers to these questions after the outpouring of Facebook comments we received to our blog post  “Who’s the most dangerous driver – Texting, drunk, high or drowsy?,” where I compared the crash risks of driving “high” to driving while drunk, driving while texting and driving while drowsy.

Many of the comments we received are related to the two questions above.  And, let’s face it, these two questions are at the heart of the marijuana debate for many. 

Question No. 1: Can a person drive after smoking marijuana?

  • Answer: Not in Michigan, at least not yet. Generally speaking, it is illegal in Michigan for a person to drive if he or she is “under the influence” of marijuana and if he or she “has in his or her body any amount” of marijuana. A very limited exception to the latter of those prohibitions is if a person is a lawful user of medical marijuana.

 Question No. 2: Is it safe to drive after smoking marijuana?

  • Answer: There is an increased crash risk for drivers who operate a vehicle while “high” on marijuana, i.e., under the influence of marijuana.

Specifically, published research has shown the following about the risk of crashing that “high” drivers face:

  • “[D]riving while cannabis-impaired approximately doubles car crash risk …”
  • A driver who is “under the influence of cannabis” is more than twice as likely to cause a fatal crash and 1.75 times more likely to cause a non-fatal crash.
  • “Marijuana users were about 25 percent more likely to be involved in a crash than drivers with no evidence of marijuana use.”

Significantly, marijuana-advocacy organizations also acknowledge a correlation (or, at least, the correlation that’s been identified in the research) between a person being “high” on marijuana and driving impairment:

  • “The responsible cannabis consumer does not operate a motor vehicle or other dangerous machinery while impaired by cannabis …”
  • “A limited number of more recent studies and reviews have postulated a positive association between presumed recent, dose-dependent cannabis exposure and a gradually increased risk of vehicle accident.”

Marijuana-advocacy organizations – as well as researchers – have even theorized about the THC levels that could result in marijuana- or cannabis-impaired driving:

‘For drivers with blood THC concentrations of 5 ng/ml or higher the odds ratio was greater and more statistically significant’”; and, “‘[S]erum concentrations of THC higher than 5 ng/mL are associated with an increased risk of accidents.’”

“The crash risk [for “drivers with THC concentrations”] begins to rise above the risk for sober drivers when a marijuana user’s THC concentrations in whole blood reach five to 10 ng/mL.”

 “Drivers with blood concentrations of 13.1 ug/L THC, or delta-9-tetrahydrocannabinol, the active ingredient in marijuana, showed increased weaving that was similar to those with a .08 breath alcohol concentration, the legal limit in most states.”

Driving free from the influence of marijuana – or any other intoxicating substance – is essential to ensuring the safety of drivers and everyone else on the road.

It’s my hope that this blog post – and the research references I will cite – provides the facts and information needed for a meaningful discussion about this important public safety issue. Next week, I’ll continue this blog post with the statistics to back up this information.

The Lawyers Corner: A recap on Michigan law, marijuana and driving 

Under Michigan law, it is illegal for a person to drive a vehicle while:

  • “[U]nder the influence of … a controlled substance” such as marijuana. (MCL 257.625(1)(a))
  • He or she “has in his or her body any amount of a controlled substance” such as marijuana. (MCL 257.625(8))
  • His or her “ability to operate [a] vehicle is visibly impaired” “due to the consumption of … a controlled substance” such as marijuana. (MCL 257.625(3))

In People v. Koon (Michigan Supreme Court, May 21, 2013, #145259), the Michigan Supreme Court ruled that the “any amount” rule as it pertained to marijuana does not apply to a registered medical marijuana patient – so long as he or she does not “operate a vehicle while ‘under the influence’ of marijuana.”

Stay tuned for my blog post next week, where I will continue this topic in more detail, and provide the sources that stated the information above.

 Related info:

 What happens when someone on medical marijuana causes a car accident? 

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