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Standardized test for marijuana intoxication still elusive

On Behalf of | Jan 30, 2018 | DUID |

The Colorado Department of Transportation says that “any amount of marijuana consumption puts you at risk of driving impaired” and warns that you cannot judge your own level of impairment. The official DUID threshold for marijuana is five nanograms of active tetrahydrocannabinol (THC), but officers are expected to base DUID arrests on the things they observe that indicate impairment.

Many law enforcement officers in Colorado are specially trained on recognizing driving impairments caused by drugs. Agencies also commonly rely on trained drug recognition experts. Among criminal defense attorneys, training programs such as Advanced Roadside Impaired Driving Enforcement or advanced drug recognition are controversial. They offer the promise of a scientific, fact-based evaluation of a person’s actual degree of impairment, but the techniques often seem to be based on relatively flimsy evidence.

At the same time, legally assuming that 5 nanograms of THC in the bloodstream implies intoxication is also problematic.

“There is no one blood or oral fluid concentration that can differentiate impaired and not impaired,” says a National Institute on Drug Abuse scientist who has spent over 20 years researching the issue. “It’s not like we need to say, ‘Oh, let’s do some more research and give you an answer.’ We already know. We’ve done the research.”

As of now, there simply is no scientifically valid method of determining someone’s impairment from marijuana. That’s partially because people react differently to THC based on gender, body-fat percentage, familiarity with cannabis and other factors.

Another reason is that legalization has allowed much more research into marijuana than was possible before. And, new research is revealing information we didn’t have before.

For example, older research suggested that, for occasional users, THC remained in the bloodstream for six to eight hours. More recently, research has made clear that the level of THC in a user’s blood reaches nearly zero within about 2-1/2 hours.

There’s no real question that cannabis is intoxicating, even for experienced users. People who are impaired by THC should not drive. Both medical and recreational users need to be aware that they risk impairment when they consume cannabis.

With no easy test to show intoxication, however, we are left with roadside tests and law enforcement’s judgment about who is impaired.