Everything You Need to Know About Stoned Driving

Up in Smoke
In 1978, when Cheech & Chong’s ’Up in Smoke’ was released, drugged driving wasn’t a hot-button topic like it is today.

Drugged, or stoned, driving has been an issue of concern for several years. The Drug Czar's office and Mothers Against Drunk Driving (MADD) recently joined together to make passage of such laws, including per se limits for blood THC levels, a legislative priority.

The success of marijuana legalization measures in Colorado and Washington has pushed concerns over drugged driving to the forefront for many. Washington's measure imposes a whole-blood THC limit of 5 nanograms per milliliter. Colorado's measure did not have such a provision but some legislators in the Mile High State have been working for years to enact such a limit and had already announced plans to reintroduce their bill before November's vote.

DUID bills in other states, such as SB 289 in California, “would allow cops to slap you with a DUI if you have even a trace of cannabis in your system.” In Montana, HB 168 would set a a 5 ng limit for blood THC levels.

Similar legislation has been defeated in Colorado, in the past, albeit narrowly; however this year's bill, HB 114, has been modified, allowing defendants “to argue in court that they - because of their size or tolerance or other factors - are not in fact intoxicated or impaired at the 5 nanograms of THC level.” This time around, the legislation has gotten a very important endorsement from the state's marijuana legalization task force, which is recommending laws and policies for the state's new industry.

A primary issue with these laws as far as cannabis is concerned has been the limit itself and whether it's inappropriately low. There's also the question of how quickly THC leaves the system, particularly for frequent heavy users. Further, blood testing is simply quite invasive. Oral fluid (saliva) testing has been suggested in the past as an alternative, but has not been used because of technical limitations. Until now.

The UK government's Home Office announced in January that it has approved the Draeger DrugTest 5000 for use in police stations around the UK. According to the Home Office news release: “Experts at the Center for Applied Science and Technology (CAST) carried out extensive tests on its effectiveness. The testing kit is able to detect THC, the active ingredient in cannabis, and is now available to police forces. Work will continue at CAST to test more equipment capable of accurately identifying other substances.”

The European Union's Project on Driving Under the Influence of Drugs, Alcohol and Medicines - known as The DRUID Project - also evaluated Draeger's device along with several others and concluded that of all the devices tested, "The DrugTest 5000 had the best overall results.” So the technology is about ready.

In terms of sheer numbers, it does appear that a lot of people drive while high. California, unlike Washington and Oregon, allows police to operate sobriety checkpoints and stop drivers randomly. If California authorities decided to approve a simple oral fluid test, like the Draeger unit, for police use, then a per se limit could prove to be a real problem for cannabis-using drivers so long as police are permitted to make traffic stops to check for sobriety without having probable cause.

Washington State's Initiative 502, complete with its 5 ng whole-blood THC per se limit, went into effect on December 6, 2012. Is the 5 ng is too low? The DRUID Project addressed that question in research published last year (go to page 83): “THC seems to be much less impairing and risky than most of the other examined substances. Although a relationship between THC concentration and accident risk was found in the epidemiological studies, it was only possible to set an exact THC cut-off by a meta-analysis of experimental studies. Thereby it was found that the serum concentration of 3.8ng/mL THC (≈2ng/mL in whole blood) causes the same amount of impairment as 0.5g/L alcohol. This value could be an empirical basis for a threshold discussion. The meta-analysis could also be used to define limits comparable to lower BAC levels.”

The DRUID research seems to support the idea that 5 ng might be appropriate; in some cases, at least, it's a starting point. Others have attempted to answer this question. Recently, a Seattle-area TV station, KIRO, performed a test with three cannabis-using volunteers, a driving instructor, a police drug recognition expert and a closed driving course. The story was picked up by outlets around the world after CNN aired an edited version of the video. The KIRO original (see below) is actually more informative, particularly when it comes to the question: How fast does THC leave the system? This is tough to say with precision because different people metabolize at different rates. There is some research which seems to show that at least, for some people, a few hours after smoking, blood THC levels drop below 5 ng. How much a person smokes, how often, the potency and the individual's metabolism are all factors.

In the KIRO video (below), Addy Norton tested at 16 ng on arrival. The other two drivers, Dylan and Jeff, were at zero. The station had arranged for fresh pipes and a quantity of Blueberry Trainwreck. The three volunteers drove the course to become familiar with it, then were allowed to smoke 0.3 grams. They were then tested. Addy's THC level had gone up to 36.7 ng, Dylan to 26 ng, and Jeff to 21.7 ng. In all, the three were supposed to consume 0.9 grams each.

Initially, all three more or less drove acceptably. Addy actually clipped a cone on her first time around the course before smoking, but the driving instructor with her didn't express any concern over that. The drug recognition expert and the driving instructor basically didn't become concerned with their driving skills until after they had consumed 0.9 grams. At that point, Jeff and Dylan displayed signs of impairment - Dylan got lost on the course on his last time around - and felt that they were too impaired to drive. Addy's performance still seemed acceptable. The DRE cop took the three through the paces of roadside and in-station sobriety tests, and agreed that all three would probably be arrested.

Addy was so entertaining during the test they asked her to smoke an extra half gram. It's funny stuff when it's a video and it's on a closed course and everyone is laughing and having a good time. However, if it was someone driving on the highway in the next lane over, it would be a lot more serious.

KIRO followed up the driving test by checking blood THC levels afterward to see how fast the level declined. Dylan's had dropped to 11.1 ng at two hours and 30 minutes afterward. Jeff was at 12.9 ng one hour and 45 minutes after the test. Addy - who showed up for the test at 16 ng - had a blood THC level of 58.8 ng one hour after the test.

The KIRO report isn't scientific research, but even so, it points out the fact that cannabis can impair driving, but that the degree of impairment after consuming the exact same amounts and potency differs from person to person - much the same as with alcohol (some people are loaded and loopy after one glass of wine, while others can seem sober and collected after half a bottle). In that sense, the blood alcohol per se laws aren't fair for everyone, but nonetheless are a standard.

Colorado's proposed DUID law allows a defense based on a lack of impairment. Someone like Addy, for example, would be able to use that news video to prove that, even at several times over the legal limit, she's a relatively good driver. Perhaps we'll end up with laws requiring police to specifically prove they had probable cause for pulling a driver over for testing in the first place. At least, we can hope.

Legal marijuana, allowed for adult social use, is going to carry with it some laws and legal standards with which marijuana users may not at first blush agree on. A blood THC per se limit for driving may be one of them. Like it or not, thanks to Washington's I-502 and Colorado's HB 114, a 5 ng THC limit is where the conversation starts.

Doug McVay

Doug McVay

Writer and KBOO radio host based in Portland, Ore. He's also editor of DrugPolicyFacts.org.