Setting an arbitrary measurement for cannabis driving impairment

Over at there are some good articles regarding current efforts in Colorado to set a THC driving limit at five nanograms per milliliter of blood — a level that, while better than the per-se laws in states like Illinois (where any detection of THC qualifies as impairment), is still far too low for many people, particularly regular medical marijuana users.

THC driving limits could cause more innocent people to spend months in jail, attorney says explores the problems of testing, the long delays in tests, and the fact that too few people in the criminal justice system have been trained to understand them.

The document above also illustrates another issue that would be amplified by the passage of a THC driving limits bill, in Bresee’s opinion. The results listed under the test name “Blood Cannabinoid Confirmation” read, “Delta-9-THC-COOH 30 ng/ml,” which suggest that the driver in question had a THC level six times higher than the proposed intoxication limit. But that’s not true, since the THC-COOH reading measures “the amount of THC that is stored in fatty tissue cells, but that isn’t active,” Bresee says.

​Department of heath tests later showed that the amount of active THC in the driver’s system (usually listed on forms as “Delta-9-THC,” sans the COOH) was six nanograms. And a private test that Bresee says is more accurate than ones the state runs — its methodology utilizes liquid, not gas, as does the CDPHE’s lab — registered the amount at just 1.5 nanograms.

Confused? So are many prosecutors, Bresee believes. [...]

In one case set in a small eastern Colorado county, Bresee says it took him more than nine months to make a prosecutor understand the relevance of active versus inactive THC.

THC blood test: Pot critic William Breathes nearly 3 times over proposed limit when sober – in this article, a medical marijuana patient has his blood tested after a night of sleep and not smoking marijuana for 15 hours.

Even when deemed sober by a doctor, my active THC levels were almost triple the proposed standard of 5 nanograms per milliliter of blood.[...]

The lab ran a serum/plasma test which showed my THC count to be at 27. According to Dr. Alan Shackelford, who ordered the blood work and evaluated my results, the number of active THC nanograms per milliliter count is about half of that total, or 13.5 nanograms of THC per milliliter of blood.

In short: If this bill passes and I was pulled over by police, I would be over the limit by 8.5 nanograms. By that logic, I would be more likely to have mowed down a family in my car on my way to the doctor’s office that day than actually arriving there safely. But I didn’t — because I wasn’t impaired.

Don’t take my word for it. According to Shackelford, who evaluated me before writing the order to have my blood drawn last Wednesday, I was “in no way incapacitated.” According to him, my test results show that it would not be uncommon to see such a high level in other people who use cannabis regularly — like medical marijuana patients. “Your level was about 13.5 for whole blood… which would have made you incapacitated on a lab value,” he said. “They need to vote this sucker down based on that alone.”

I’m all in favor of getting drivers off the road when they’re impaired, but a test that doesn’t actually determine impairment and will sweep up non-impaired drivers into the net is not at all helpful.

It seems to me that the best option may be a combination of videotaped field roadside sobriety tests plus blood testing, along with good judgement. The notion that at at x nanograms you’re OK, but x+1 nanograms and you’re impaired (particularly when that result can mean years of prison) is absurd.

Now if you have a videotaped sobriety test and the driver is staggering around with slurred speech and eye-hand coordination problems and the test comes in with significant THC presence, then I think a judge or jury can readily determine impairment. If, on the other hand, the person seems able to perform all requested sobriety tasks competently despite having a high THC blood level, and perhaps is able to show through subsequent testing that her regular use (as a patient or not) brings her levels up higher, then a judge or jury can rightly say that she was not impaired.

These are human beings, not machines.

Since the cause of most crashes is fatigue, I wonder why the legislature isn’t setting a legal limit on the levels of adenosine in the body.

[Thanks, Cliff]

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