Currently Reading: Nanogram Nonsense

Setting a definitive limit for nanograms of THC in your blood in order to drive is not medically supported.

One of the touchiest and most complicated issues in the entire medical cannabis world is driving under the influence, or DUIs. While it’s always been against state law to drive while impaired by any substance, the cannabis DUI — or “green DUI,” as some call it — has gotten a lot of attention lately because of recent attempts to set a legal limit of THC in a person’s blood as well as because of Initiative 502, which, if voters approve in November 2012, would set an absolute bright line limit for THC blood levels and driving.

That limit would be 5 nanograms of active metabolite of THC per milliliter of blood. Some in the medical cannabis community argue that that limit is far too low and that it doesn’t equate to impaired driving. They also note that the research base on the issue is far too cloudy to set definitive levels, especially ones that could potentially jeopardize someone’s mobility.

Proposed per se standards for THC are both arbitrary and unnecessary,” NORML’s deputy director Paul Armentano recently told the Washington State Legislature. “They are arbitrary because there is little, if any, scientific evidence to consistently correlate THC or THC metabolite blood levels with psychomotor impairment.”

Translation: human beings vary widely in how their bodies process THC, too much so to set an absolute level for what constitutes THC-impaired driving.

One local physician, Gil Mobley, recently helped a dozen area medical cannabis patients get their THC levels tested in a relatively scientific manner and under a variety of conditions. The results, to be released publicly this year, surprised even Mobley.

“We were surprised by how high some patients’ levels were,” says Mobley.

He notes that patients who had abstained from cannabis use overnight were still seeing THC levels of 10 to 20 nanograms per milliliter when blood draws were done in the morning. These medical cannabis patients, he says, typically medicate several times a day for chronic pain issues and their “background” levels were quite high.

So how impaired were they?

“They were fine when they came in with a background level of 10,” says Mobley, who oversaw the administration of standardized impairment tests to the dozen patients. “They were fine after they medicated and when their THC levels skyrocketed to 140. They were fine on 100 percent of the tests. Later in the day, some had deficiencies on recall tests, but that was likely because they were tired.”

Mobley says that his own reading of the research literature shows that regular cannabis users will have elevated background THC levels even hours after medicating. One patient who was tested had not smoked cannabis for 48 hours and still tested at 5 nanograms. Another patient tested at 0 NG/ML an hour after medicating, likely owing to a very high metabolism, says Mobley. Others tested in the 40 nanogram range and above, never falling below 10 nanograms hours after medicating.

With a 5 nanogram per se limit, they would almost all be technically impaired and could lose their driving privileges and could also face stiff legal penalties. That should concern everyone.


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