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THC Limits Not Correlating With Driving Impairment

 Posted on May 06, 2019 in Uncategorized

Roadside oral indicator tests are commonly used across North America and around the world to determine whether someone has drugs in their system, but what do they really show?

When you’re pulled over driving your vehicle and the police officer or trooper thinks you may be under the influence, a breath analyzer test could be used in conjunction with sobriety tests to determine what level of alcohol you have present in your system and whether or not you have an impaired ability to drive. As the legalization of both medical marijuana and recreational marijuana continues across North America, more and more law enforcement agencies are looking at ways to combat drug driving or drivers driving their vehicles under the influence of marijuana. However, detecting drugs in someone’s system isn't the problem. It’s determining whether the levels of drugs in someone’s system have impaired their ability to operate a motor vehicle. Roadside saliva tests don’t tell you how much of a particular drug you have in your system, how high you are, whether you’re impaired or how impaired you may be. They are just an indication that drugs are present at some level in your system.

When these roadside drug tests return a positive indication, people are then charged, and a blood test may be taken to determine how much of a substance is present inside their system. The problem is that this system could be fundamentally flawed.

What Are They Testing For?

The psychoactive compound inside cannabis responsible for getting you high is known as tetrahydrocannabinol or THC. THC is one of the two main cannabinoids found in marijuana and is responsible for the euphoric high many people experience when they consume or smoke cannabis.

The effects of THC on you can last anywhere from 1-2 hours through to 6-7 hours depending on what you consumed, how you consumed it, how potent the marijuana was and what your tolerances are. THC and other compounds can build up in your system to varying degrees.

Three of the different ways which THC can be detected in the system, saliva or oral fluids, blood samples and urine samples. THC levels can be detected at varying times and strengths depending on which testing method is utilized.

What Were Their Recommendations?

According to recommendations made by a state-appointed traffic safety task force in Michigan, the presence of THC in the blood isn’t correlating to driving ability or performance. The report which was issued by the Michigan Impaired Driving Safety Commission found that blood levels weren’t associated with behavioral impairment, and different amounts of the compound found in different peoples blood work produced varying degrees of impairment and issued the following statement:

“The Commission recommends against the establishment of a threshold of delta-9-THC bodily content for determining driving impairment and instead recommends the use of roadside sobriety tests to determine whether a driver is impaired.”

Their findings are similar to other findings which were issued by the National Highway Traffic Safety Administration, American Automobile Associations and other safety experts that advise against per se thresholds for THC. The Commission also went further and stated that people driving under the influence of cannabis:

“typically drive slower, keep greater following distances, and take fewer risks than when sober.” They also added that “While there is some uncertainty as to the crash risk associated with cannabis impairment alone, the research is clear that the risk is lower than that of alcohol impairment.”


Currently, there are five states which impose various per se limits for the detection of specific amounts of THC in blood, Montana, Nevada, Ohio, Pennsylvania, and Washington. A further eleven states Arizona, Delaware, Georgia, Illinois, Indiana, Iowa, Michigan, Oklahoma, Rhode Island, Utah, and Wisconsin, impose zero tolerant per se standards.

In those states, it is a criminal violation of the traffic safety laws to operate a motor vehicle with detectable levels of THC in your blood. Colorado law infers driver impairment occurs when THC is detected in blood at levels of 5ng/ml or higher.

Unfortunately, there are no easy ways to determine how long THC stays in your system. People process the cannabinoid differently, and different strains and consumption methods have different effects. No matter what the circumstances are, waiting until all traces of THC have left your system is the ultimate way to ensure you have no problems when operating a motor vehicle.

If you have been arrested for any marijuana-related offense, please contact Fort Worth Criminal Defense Attorney Craig Dameron at 817-222-0624.

A huge thank you to marijuana author Ben Johnson for submitting this excellent article!

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