How will police around Lake Tahoe determine if a driver is stoned? |

How will police around Lake Tahoe determine if a driver is stoned?

Claire Cudahy
Law enforcement officials say field testing is an accurate way to determine if a driver is impaired by marijuana.
Getty Images / iStockphoto | iStockphoto

Determining if a driver is high on marijuana is not as simple as determining if someone is drunk — or it is, depending on who you ask.

As California and Nevada work to release state regulations regarding the recent legalization of recreational marijuana, the best practices for determining whether a driver is under the influence of marijuana are being studied and tested.

“It’s not like testing for an opiate or alcohol — those are very straight forward scientific tests, and we can correlate what we find in the blood or urine or body fluids with a dosing that degrades at a very predictable level,” Barton Health’s Dr. Sherellen Gerhart said at the recent Tahoe Regional Young Professionals town hall on recreational cannabis.

“Cannabis is a very complicated compound that has anywhere between 80 and 120 ingredients depending on the plant or the product, and the degradation of those products depends on the delivery system. Having cannabinoids in your system does not mean they are active or that you’re intoxicated, so this is a very complicated issue.”

An issue, said Gerhart, that needs to be studied more.

According to Lori Ajax of California’s Bureau of Medical Cannabis Regulation — soon to be Bureau of Cannabis Control — the state is currently one year into a three-year study that seeks to better understand how marijuana affects motor skills.

“Sometimes what we use to determine alcohol impairment doesn’t work the same way with cannabis,” said Ajax. “There’s a lot of private companies in California that want to do this research, but it’s just how can they legally have that cannabis in order to do that research.”

Marijuana’s federal classification as a Schedule 1 drug — alongside substances like heroin, LSD and MDMA — is a major impediment to accessing it for research.

California is looking into a licensing system that would aid in helping private companies get small amounts of cannabis for research and development, said Ajax.


At present, California does not define specific levels of THC — the psychoactive element of marijuana — in the blood stream to qualify as under the influence. In Nevada, the level is 2 nanograms of THC per milliliter of blood.

While both of these thresholds could change once the new state regulations are released, critics of the blood test argue that due to the complicated biology of THC and the unpredictability of how it clears from our systems, the results are not always accurate. For instance, a heavy marijuana user could test over the limit without having consumed marijuana in weeks, while in an occasional user, THC could clear out of the blood in just a couple of hours and the driver may still be impaired.

But according to one Nevada Highway Patrol trooper, determining if someone is fit to drive is much simpler than a blood test.

“One of the common misconceptions about the marijuana law is that everybody thinks everything is going to change. Nothing changes with us,” said trooper Dan Gordon, NHP spokesman for Northern Nevada. “We look for driving patterns — following too close, speeds too fast, too slow, can’t stay in a travel lane — there’s just a myriad of things we look for when it comes to identifying impaired drivers.”

From there, said Gordon, it’s a field sobriety test.

“We are looking for balance, their ability to walk in a straight line, but more importantly we are looking for them to be able to multitask and see how they do when we give them what we call ‘divided attention tests,’” explained Gordon.

“And from that point on we do have some road-side testing as far as a mouth swab, and then we have a couple of additional tests we can do for marijuana specifically, but the average officer, trooper or deputy with standard field testing is going to be able to identify if someone is impaired or not.”

Once the driver is placed under arrest, the usual protocol is a blood test.

“We don’t do too much with urine because urine doesn’t give us a number. It’s a positive or negative thing,” said Gordon.

Trooper Ruth Loehr of California Highway Patrol said the majority of the troopers in South Lake Tahoe are “drug recognition experts,” which comes with additional training, and rely on field testing before making the arrest.

“We are going to look at the driver’s appearance, their speech, their physical appearance, their eyes, and smell is certainly a factor,” said Loehr.

Some jurisdictions in California, however, have turned to new technology to determine if a driver has used marijuana. In San Diego, police can now test for the presence of seven drugs using a mouth swab and the Dräger DrugTest 5000 — which runs for about $6,000. This tool cannot determine the level of intoxication, just whether the drug is present.

Ultimately, Loehr said she is concerned with how the legalization of recreational marijuana will play out on the roads.

“I think that people are not aware of how it affects them. We are talking psychophysical,” said Loehr. “They may think they are fine to drive, but they aren’t.”

California draft regulations on recreational marijuana are expected to be released in September, while Nevada hopes to have its regulations in place by June.

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