1, 2, 3 or 5 Nanograms? DUI-Rules Need Standards | Marijuana

1, 2, 3 or 5 Nanograms? DUI-Rules Need Standards


Since the worldwide liberalization of cannabis, the debate surrounding a reasonable THC limit while driving is intensifying in many countries. On the same token, countries enforce varied national regulations when it comes to DUI-driving. Thus, each country determines exactly how much THC must be present in your system to be considered “intoxicated” or “impaired.”

In the U.S., many states with legalized cannabis have established a maximum limit of five nanograms of active THC in the system. Canada will only set precise limits when they finalize their legalization, and the regulations across Europe vary greatly. While only active THC is measured in most parts of Europe and the USA, the non-psychoactive metabolite THC-COOH also plays a role in driving impairment in some EU countries and a few US states. In some countries, a salivary or urine test is mandatory before blood testing, in others, pre-testing is voluntary, and elsewhere, only the trained eye of the police and the blood parameters count. However, in all countries mentioned, only the blood parameters can serve as court evidence. The penalties are usually fines or driving bans that can last many years if not an entire lifetime.

Germany has the strictest per se limit

In Germany, the number of cannabis consumers ordered to carry out a drug test has steadily increased since the mid-1990s. If more than 1 nanogram(ng) of active THC is detected in a roadside blood serum test, the driver’s license will be withdrawn by the driving license authority. The German limit is the strictest in comparison with other countries which have defined a per se value, and not only because 1ng THC causes no observable effects. While most countries’ measurements are determined in total blood — nanograms of THC per milliliters of blood — the Federal Republic of Germany, on the other hand, measures the THC content in the blood serum only, which leads to a nanogram count more than twice as high.

Even Switzerland, which has a precisely defined law for DUI-offenses, has a much higher limit. The Swiss limit is 1.5 ng THC in total blood. At first glance, the German limit of 1 ng/ml appears very similar. If, however, the fact that the Swiss limit value is determined in total blood and not in the serum, a limit value of 3 ng/ml of serum is calculated. With this adjustment, the limit in Switzerland (according to German reading) is closer to 3 ng.

It is also controversial to determine a precise THC-COOH value, which could shine a light on consumption intensity and thus the frequency of marijuana use. “Until now, it was considered certain that at least the detection of specific metabolic products of the cannabis main active substance THC in the hair proves a consumption without doubt. A researcher at the Institute of Legal Medicine at the University Hospital of Freiburg around the toxicologist, Prof. Dr. Volker Auwärter has established through experimental work that this conclusion is not permissible,” the “Scientific Reports” wrote in October 2015. Also, some US states, including some that have legalized marijuana for medicinal use, have zero-tolerance laws for marijuana-influenced driving, which makes the presence of THC-metabolites (which can linger for weeks after use) illegal.

Which limit applies where?

Austria: No specific limit, any “impairment,” blood test if suspected

Belgium: 1ng/ml blood

Croatia: No specific limit, any “impairment,” blood test if suspected

Cyprus: No specific limit, any “impairment,” blood test if suspected

Czech Republic: 2ng/ml blood

Denmark: 1ng/ml blood

Estonia: No specific limit, any “impairment,” blood test if suspected

Germany: 1ng in the blood’s serum, equivalent to 0.5ng in the system. THC-COOH testing

Finland: No specific limit, any “impairment,” blood test if suspected

France: No specific limit, any “impairment,” blood test if suspected

Hungaria: No specific limit, any “impairment,” blood test if suspected

Ireland: 1ng/ml blood

Italy: No specific limit, any “impairment,” blood test if suspected

Latvia: No specific limit, any “impairment,” blood test if suspected

Lithuania: No specific limit, any “impairment,” blood test if suspected

Luxembourg: 1ng/ml blood

Malta: No specific limit, any “impairment,” blood test if suspected

Netherlands: No specific limit, testing only at random

Norway: 0.4-1 Micromol/ml (not Nanogram)

Poland: No specific limit, any “impairment,” blood test if suspected

Portugal: No specific limit, any “impairment,” blood test if suspected

Switzerland: 1.5ng/ml blood

Romania: No specific limit, any “impairment,” blood test if suspected

Slovenia: No specific limit, any “impairment,” blood test if suspected

Slovakia: No specific limit, any “impairment,” blood test if suspected

Sweden: No specific limit, any “impairment,” blood test only if suspected

Slovenia: No specific limit, any “impairment,” blood test if suspected

United Kingdom: 2ng/ml blood

Canada and The United States of America

Canada: Currently no limit, impairment has to be proven in court. Planned for 2018:

  • 2 ng but less than 5 ng of THC/ml: Having at least 2 ng but less than 5 ng of THC per milliliter (ml) of blood within two hours of driving would be a separate summary conviction criminal offense, punishable only by a fine. This lower level offense is a precautionary approach that takes into account the best available scientific evidence related to cannabis. This offense would be punishable by a maximum fine of up to $1,000.
  • 5 ng or more of THC/ml: Having 5 ng or more of THC per ml of blood within two hours of driving would be a hybrid offense. Hybrid offenses are offenses that can be prosecuted either by indictment, in more serious cases, or by summary conviction, in less serious cases.
  • Combined THC and Alcohol use: Having a blood alcohol concentration of 50 milligrams (mg) of alcohol per 100ml of blood, combined with a THC level greater than 2.5 ng per ml of blood within two hours of driving would also be a hybrid offense.

USA: Limits vary across states

Standards in states where cannabis is illegal

Montana: 5ng/ml blood

Ohio: 2ng/ml blood

Pennsylvania: 1ng/ml blood

Standards in states where cannabis is legal

Washington State: 5ng/ml blood

  • Drivers with less than 5ng/ml of blood can still be sentenced for driving “affected by” cannabis when independent evidence proves driving skills were diminished “to an appreciable degree” by the THC in the suspect’s system.

Colorado: 5ng/ml blood

States with legal Cannabis and without per se standards

Alaska: No specific limit, blood test if suspected

California: You are considered to be “under the influence” of marijuana in California when:

  • You are impaired as a result of marijuana consumption
  • There is an obvious impairment of mental or physical abilities
  • You can no longer drive a vehicle with the caution of a sober person, using ordinary care, under similar circumstances

Oregon: The prosecutor must prove that the driver was “adversely affected to a noticeable or perceptible degree by cannabis.”

Nevada: 2.0 ng/ml blood

Massachusetts: No specific limit, blood test if suspected. A person is suspected of driving “under the influence” if cannabis consumption “diminished the person’s ability to operate a motor vehicle safely.”

Maine: 5.0 ng/ml blood

District of Columbia: The prosecutor must prove that the driver was “adversely affected to a noticeable or perceptible degree by cannabis.”

States where any THC-traces in your system will cause legal trouble:

Arizona, Delaware, Georgia, Illinois, Indiana, Iowa, Michigan, Oklahoma, Rhode Island, South Dakota, Utah, and Wisconsin.

Experts call for an adjustment

Professor Auwärter, who advises the German Federal Government as a member of the expert committee on DUI questions, criticizes the lack of a scientific b+. In one case of a quasi-ineffective amount of THC in a driver’s system, the withdrawal of their license was pending. On the one hand, 0.05 percent alcohol in the system is legal yet doubles the accident risk compared to 0.00 percent alcohol in the system. For THC, even after any psychoactive effect is long gone the applicable limit remains at 1 ng of blood serum, Auwärter states. According to Auwärter, cannabis-influenced drivers cause far fewer accidents than drunk drivers.

Cannabis, unlike alcohol, does not lead to disinhibition — a lack of restraint manifested in disregard for social conventions, impulsivity, and poor risk assessment. The ability to decide to stay sober and drive or smoke marijuana and walk is not influenced by cannabis ingestion. Additionally, a cannabis-influenced driver was shown to be much more cautious than an alcohol-influenced individual, as Auwärter pointed out in 2014 during the meeting of the city of Frankfurt on the subject of cannabis model projects. Auwärter considers the current THC limit to be too low. In an Interview with “Süddeutsche Zeitung,” Auwärter called for an adjustment to “2-5” ng/ml of blood.

DUI on the bicycle

In Germany, the same DUI-related rules apply to cyclists and automobile drivers. Anyone who rides a bicycle under the influence of cannabis can lose their driver’s license. Dr. Benno Hartung and scientists from the University of Düsseldorf wanted to know more precisely whether cannabis-influenced cyclists are truly as dangerous. The scientists observed 14 people before and after the consumption of one, two, and then three joints on a bicycle course designed to test their riding ability under the influence of cannabis. All subjects were regular cannabis users who claimed to consume between one gram per week and one gram per day. In total, the participants were allowed to smoke 38 Bedrocan joints, and complete the course again after each joint. In the evaluation, the scientists could not recognize any differences in driving style. Whether one, two or three joints were smoked, the bikers mastered the course just as easily as before the consumption of cannabis.

Hartung, however, warns not to overestimate the results because the study is not representative due to its low number of participants. At the same time, he criticized how it is very difficult in Germany to receive support for realistic studies on the effects of illicit drugs in road traffic.

About Author

Michael Knodt is an expert on cannabis politics and cannabis culture across Europe. Born in North Germany, Michael has been living in Berlin since 1990. He initially studied history and journalism before receiving his certification as a carpenter. Since then, Michael has made regular visits to countries where cannabis is cultivated, such as Jamaica and Morocco. He has worked as a freelancer for Weedmaps, Vice Magazine Germany, Sensi Seeds and numerous German-language cannabis magazines since 2004. From 2005 to 2013, Michael was the Editor-in-Chief of Germanys biggest cannabis periodical. He also is the face and presenter of the most popular program on cannabis prohibition and just launched a new channel called "DerMicha." Aside from his journalistic work, Michael is a cannabis patient, activist, sought-after speaker on conferences and congresses, and a father of two.


  1. Per se laws specifying a maximum THC blood levels have no basis in science.  The NHTSA acknowledges that THC levels in the body do not reliably predict impairment. Instead, we should measure actual impairment.  

    I have developed an app called DRUID (an acronym for “DRiving Under the Influence of Drugs”), now in the App Store for the iPad and iPhone (Android version coming soon). DRUID measures reaction time, hand-eye coordination, balance, time estimation, and decision making and integrates all the measures into an overall impairment score. DRUID demonstrates that measuring marijuana impairment is available now.  The app also permits individuals to assess their own level of impairment (or that of the designated driver) and determine whether they are impaired.  See more at http://www.druidapp.com

    DRUID was featured on All Things Considered: https://www.npr.org/2017/01/25/511595978/can-sobriety-tests-weed-out-drivers-whove-smoked-too-much-weed

    and on television: https://sacramento.cbslocal.com/2017/02/28/science-lags-behind-marijuana-impairment-testing/

    After getting my Ph.D. at Harvard, I have been a professor in the Psychology Department at UMass/Boston for 40 years, with a specialty in research methods, measurement and statistics.

    Michael Milburn, Professor
    Psychology Department

  2. Thank you, I have been preaching this for a while. The idea that a numerical stat will show an individual is impaired is a holdover from alcohol. While there are accepted levels in the blood for alcohol it is not the same for cannabis.
    Impairment has to be determined by roadside evaluation. The police don’t like that it takes more personal time. It also requires integrity which is in short supply in too many jurisdictions.

  3. Thank you so much for this comprehensive piece!!! It is very informative and highlights how the approaches can be so variable because the biologic measures are not linearly related to function. Objective, simple, quick, sensitive and specific tests of impairment of functions considered critical for driving are despartely needed. The DRUID test and another test with a similar concept; MyCanary are good means to assess and highlight to individuals- aspects of cognitive status and changes with marijuana use, that can occur with cogntivie functions. The tests of saliva are being used in several countries and the test of saliva, Draeger 5000 was accepted for courtroom use on a case in California. But functional tests are still needed.

    Our company is using an approach that capitalizes on the retinal ganglion cell dysfunction that occurs with marijuana use. It also is an app, but for law enforcement use. The test is IMMAD- Impairment Measurement Marijuana and Driving. The science is complex, but the test is short, objective, simple and initial data is indicating it to be very sensitive to cannabis use and adjustments are indicative of it being specific to marijuana impairment. Data out of the state of Washington is indicating that those testing positive to marijuana alone, no other drugs or alcohol, are five times more likely to have killed someone other than themselves compared to a person testing positive to alcohol. This means a pedestraian, bicyclist or someone in another vehicle. While there clearly are fewer deaths related to cannabis impaired driving compared to alcohol, the data is pointing to the potential that a marijuana impaired driver is missing aspects of the road and surrounding. IMMAD tests this. Initial data is documenting the tunnel vision that is often described by marijuana users. Ironically the test evolved after decades of my having provided clinical services specific to vision impaired driving, assessment of fitness to drive in elderly and another decade of Alzheimer’s related research.

    No test of function will give a complete picture of the impairments to drive with marijuana use. But clearly tests of function need to be available. The training officers use related to DRE or ARIDE certainly have done much to help manage marijuana and its impact on driving. But additional tools are needed. IMMAD is such a technology.

    • Neil Woodward on

      “Data out of the state of Washington is indicating that those testing positive to marijuana alone, no other drugs or alcohol, are five times more likely to have killed someone other than themselves compared to a person testing positive to alcohol.”: ???
      “Data” showing that marijuana is FIVE TIMES as dangerous as alcohol? Bring your “data” out, Mr. “Expert” and let’s have a look at it! You can’t be serious!

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