Before Colorado legalized recreational use of marijuana in 2012 and its sale in 2014, drug tests didn’t need to distinguish between usage one month ago or one hour ago. Now, labs and police are using new methods to find out when and how much you’ve taken, particularly if you’re involved in an auto accident.

Colorado Officials Continue to Look for Reliable Test Standards

The marijuana dispensaries offering smokable and edible options that line Colorado streets opened their doors three years ago, and although pot is legal, laws prevent usage in certain situations, such as driving. How do current tests measure the marijuana in your system? Can they tell when you it entered your system and how much?

The possible answers and the ways to measure chemical levels continue to change as Colorado and other parts of the nation adjust to the reality of legalized marijuana.

Testing a suspect for marijuana was relatively easy before the state legalized recreational use in late 2012 and sales in 2014. Before legalization, the presence of marijuana trace chemicals in the bloodstream was evidence of illegal drug use; the amounts and types hardly mattered. Now that Colorado has legalized marijuana, police officers and prosecutors who want to prove that a motorist was driving while impaired must show that a driver had used marijuana recently enough to be impaired. The trick is testing for the right chemical.

Authorities previously tested urine for a marijuana trace chemical called THC-11-oic acid which doesn’t even get users high but remains in the system for up to a month after usage. According to The Denver Post’s David Migoya, laboratories found better indicators for recent pot intake and impairment by focusing on other byproducts of THC, the drugging chemical in marijuana.

Toxicology laboratory owner Sarah Urfer told The Post:

“Nobody thought it mattered what you were looking for…Early on, scientists didn’t know for sure which of the cannabinoids were responsible for impairment. They’d measure carboxy and try to correlate it to impairment.”

Her Boulder lab, ChemaTox, conducts DUI screening for nearly 75 percent of Colorado’s law enforcement agencies.

Because marijuana intoxication is so different from alcohol intoxication, authorities have had a difficult time determining a reliable benchmark. Pot effects also vary with the type of usage, The Post reported. The effects of smoking disappear much more quickly than the effects of eating marijuana-laced foods. What has law enforcement officials concerned, though, is when drivers have been using both marijuana and alcohol. The Colorado Department of Transportation reported that about 36 percent of drivers in fatal car accidents in Colorado who had been using pot had also been drinking alcohol.

States Use Different Approaches

Colorado has an established blood level benchmark for charging a driver with DUI, but passing that threshold, called a “permissible inference” of impairment, isn’t enough in and of itself to convict a driver, The Post reported. A judge or jury decides whether the driver was impaired.

Montana and Washington, however, treat the same THC level as if it were blood-alcohol level, where prosecutors need no further proof to show impairment and convict a driver of DUI.

Twelve other states, including Arizona and Utah, have zero-tolerance policies, meaning any level can be used for a conviction.

Meanwhile, the National Highway Transportation Safety Administration questions the effectiveness of most DUI detection methods and interpretations, pointing to variables in toxicology testing and in how THC affects drivers, The Post reported. The agency recently told Congress that the THC levels that states use to charge drivers are “artificial” and based on something besides science. You can read up on the latest science news at

The Race for a Test

Private businesses are queuing up to provide reliable answers. Oakland, Calif.-based Hound Labs and Vancouver, B.C.-based Cannabix Technologies are two companies developing hand-held-devices that detect both marijuana use and alcohol consumption, CNN reported. As with other breathalyzer devices, test subjects blow into a tube, and the machine gives instant results.

The devices show blood-alcohol levels but only offer yes/no results for the presence of THC. That limited information might be a selling point. The pot indicator, which doesn’t even distinguish between types of THC, gives a yes indication only if the subject has smoked pot within the past two hours or so. That recent use factor might be the clearest of all indicators of mental impairment.

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