When is a person 'too high to drive'?
By Larry Gabriel
December 29, 2010
It should have been easy to see that driving under the influence was
going to come up when voters gave the thumbs up to medical marijuana
in Michigan. Marijuana is an intoxicant that has some effects similar
to alcohol and opiates. It would seem to be a good thing for medical
marijuana patients to not drive while under the influence of the
medication. That's a matter of public safety, and not just because
police have been reported to lay in wait near compassion centers
where marijuana smoking takes place in order to arrest drivers
suspected of intoxication. Other patients have been charged with DUI
after having been stopped for other traffic violations and divulging
that they were medical marijuana patients.
"There are some things you don't need to tell, don't have to and
shouldn't," says Brandy Zink, a spokesperson for the Michigan Chapter
of Americans for Safe Access, a pro-medical marijuana organization.
Hmm, maybe a variant on the old Don't Ask, Don't Tell policy for gays
in the military is pertinent to the medical marijuana patient.
Zink notes that the odor of marijuana in your vehicle is probable
cause for police to suspect intoxication, and the presence of
marijuana might give police a clue. Either of those things could lead
to a blood or urine test to figure out if you've ingested marijuana.
Bad behavior might qualify you for closer scrutiny too.
This is way more complicated than it sounds and prompts a lot of
questions that have not been answered on the legal tip. For instance,
police test drunk-driving suspects for alcohol, the intoxicating
ingredient in beer, wine and distilled spirits, in their blood. A
blood alcohol content of .08 or higher makes you a drunk driver in
Michigan. When it comes to marijuana, a legal limit for the presence
of THC hasn't been established. What's more, the majority of
marijuana tests are for metabolites created from marijuana as the
body processes it; they mostly do not test for THC, the part of
marijuana that gets you high. While some tests do identify the THC
level, most tests are for 11-COOH-THC (also known by several other
names), a byproduct metabolite that does not get you high but stays
in the body much longer than the psychoactive ingredient.
Under the prohibition-zero tolerance approach, police need only prove
the presence of these metabolites to establish that someone had used
marijuana. This is fairly new territory. For law enforcement in the
past, the focus was on arresting users for possession, not for
In June, the Michigan Supreme Court ruled that, for registered
medical marijuana patients, the presence of byproduct metabolites was
not proof of intoxication at the time of citation although there
have been cases where police have charged drivers with medical
marijuana cards for the presence of marijuana metabolites other than
THC in their bloodstream since then. None of them have made it to trial.
Still, how does ingesting marijuana affect driving? In the past,
there was no reason to figure out a level where legal impairment
begins. Now medical marijuana patients want to know: How long do I
have to wait before I can drive?
There is no established level of THC at which you are legally
impaired for the purpose of driving. However, there are lots of
opinions by experts and others involved. Attorney Matt Abel, of
Cannabis Counsel TLC, says that THC, the substance in marijuana that
gets you high, is out of your bloodstream in "four to six hours,
although that doesn't mean someone has to wait that amount of time
before they drive."
That seems based on the alcohol model where there is an established
legal level. Paul Armentano, deputy director of the National
Organization for the Reform of Marijuana Laws and expert witness on
marijuana science issues, begs to differ. Armentano says THC
intoxication for smoked marijuana has "about a two-hour window. If
administered orally, we could be talking as long as four hours. This
is a subject that has been studied. I'm taking calls on this subject
every day now."
Armentano has also studied up on motor impairment caused by
marijuana. "Acute intoxication from marijuana that could adversely
affect motor skills lasts about 60 minutes. A study published just
this past year on psychomotor impairment said that experienced users
of the drug really didn't perform differently after they used marijuana."
Indeed, a study published this past fall in the journal
Psychopharmacology, titled "Tolerance and cross-tolerance to
neurocognitive effects of THC and alcohol in heavy cannabis users,"
reported: "In conclusion, the present study generally confirms that
heavy cannabis users develop tolerance to the impairing effects of
THC on neurocognitive task performance. Yet, heavy cannabis users did
not develop cross-tolerance to the impairing effects of alcohol, and
the presence of the latter even selectively potentiated THC effects
on measures of divided attention."
Basically, they found that while drivers who smoked marijuana did not
perform that badly on driving tests, adding alcohol to the mix was
really bad. Nobody is saying that it's OK to drive while impaired by
marijuana. However, when compared to alcohol use, the harms were much
less. Or as Abel puts it, "marijuana is way safer than alcohol."
A 2007 research report from the Society for the Study of Addiction,
"Developing limits for driving under cannabis," suggests a THC level
of 7 to 10 nanograms per milliliter, which is analogous to .08
percent blood alcohol content in terms of driving impairment.
But that just addresses the high. There are actually some 400
different chemicals in marijuana, and indications that some of them
are useful in treating some 30 different ailments. This prompts a few
more questions from Abel: "What gives you the munchies? What relieves
spasm? What causes short-term memory loss?"
Good questions all. They'll be addressed soon in another column.