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Should Alcohol and Cannabis Have Separate DUI Laws?

June 21, 2017
Should Alcohol and Cannabis Have Separate DUI Laws? A Former Officer Weighs In(kali9/iStock)
When it comes to the perils of cannabis and driving, there’s a lot to take into consideration. In an illegal state, getting caught with cannabis in the car can easily earn you a possession charge. Consumers in legal states face risks as well; charges of driving under the influence of cannabis can occur regardless of whether or not the driver is impaired. Many tests to detect THC levels in one’s system don’t account for the length of time cannabis metabolites remain in human cells, which means a driver may not have consumed cannabis in weeks but can still retain enough THC in their body to be found guilty of a DUI.


How long does THC stay in your system?

To further discuss the idiosyncrasies of driving and cannabis, we reached out to Scott Leist, a former Seattle police officer and criminal prosecutor who is now a defense attorney with Washington Traffic Defense, to get his perspective on the complexities of driving with cannabis in the car and driving under the influence of cannabis.

Leafly: How would you interpret cannabis DUI laws, compared to other current alcohol or substance-related regulations?

Scott Leist: In Washington, the DUI (driving under the influence) laws related to marijuana are problematic. The legislature tried to create a per se legal limit, like the .08 limit for alcohol, without accounting for the fact that THC is nothing like alcohol.

“Some studies suggest that driving with moderate levels of THC in one’s system can actually improve driving performance.”
Scott Leist, Washington state defense attorney

First, THC obviously affects the body differently in terms of “intoxication.” In fact, some studies suggest that driving with moderate levels of THC in one’s system can actually improve driving performance (less risk taking, slower speeds, less aggression). No scientific study suggests that is true with alcohol.

Unlike alcohol, where the .08 limit was based on years of experience, medical data and some marginally “scientific” studies, the THC blood limit of 5ng/mL is completely arbitrary. There is simply no good science suggesting that 5 ng/mL is “impairing” or what amount would be “impairing.”


How Does Alcohol Affect THC Blood Concentration?

Can you explain why a lack of distinction between alcohol and THC is problematic?

Unlike alcohol, THC doesn’t quickly and completely metabolize.

For example, if I go out and have three beers of a known alcohol concentration, it’s pretty easy math to figure out my blood/alcohol level and how long it will take before it is all metabolized. THC, on the other hand, can be present, at somewhat low levels, long after one is completely sober.

How fast and how completely THC metabolizes depends on:

  • How it was ingested,
  • The time since ingestion,
  • Whether the person is a regular (frequent) or heavy (dosage) user of marijuana; and
  • The concentration of THC.

Cannabis Is Exactly 114 Times Less Toxic Than Alcohol

Small levels of THC can be present days or even weeks after ingestion, sometimes bringing someone who is completely sober close to or even over the 5 ng/mL limit long after they are sober.

“Keep it closed, put it in the trunk or other inaccessible part of the car and don’t imbibe while driving.”
Scott Leist's advice on transporting cannabis when driving.

Unlike alcohol, there isn’t a way to calculate how a certain item will affect an individual person. I know you can buy marijuana and the vendor will tell you the THC percentage, but there is no way to accurately predict, with any certainty, what that person’s blood THC level will be over time.

What is a “serving” of a marijuana brownie? What is the marijuana equivalent to “two beers?” How much THC for me, at my weight and age, will get me to a 5 ng/mL, level and how fast and how long will it take to wear off? Nobody knows. Alcohol allows for much more exact predictions.

Are there accurate field tests for THC intoxication?

Police officers don’t have a lot of experience or training for marijuana DUI detection. They don’t have a battery of field tests that they can go through to confirm or dispel their suspicions. They generally decide whether someone is DUI for THC based on:

  • The driving,
  • Observations (smell of marijuana, presence of marijuana/smell in the car),
  • Physical signs, (which can be as simple as red eyes); and
  • Any admissions to recent use.

So you can end up with VERY thin arrests. Then the only step they can take is a blood test, which generally requires a search warrant.


Blood Testing Drivers for THC is Nonsense, AAA Study Says

Finally, unlike alcohol, there is no way to personally check yourself to see if you have had too much THC. There are no breath tests for THC impairment. You generally can’t give yourself the field sobriety tests (walk & turn, etc.) like you can with alcohol to see how affected you are. Nobody falls down or throws up from THC (at least to my knowledge), making it harder for others to take your keys away.

Are there any best practices that you would recommend for those traveling with cannabis in the car?

Transporting THC in one’s car should look a lot like transporting alcohol. Keep it closed, put it in the trunk or other inaccessible part of the car, and don’t imbibe while driving.

People should also remember that while marijuana might be legal in your state, it is still illegal federally and in many other states, so don’t “forget” that you have marijuana in your glove box or a pipe if you are heading over a border.

Lisa Rough's Bio Image

Lisa Rough

Lisa is a former associate editor at Leafly, where she specialized in legislative cannabis policy and industry topics.

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  • There is certainly differences in the science used for drivers having to fightDUIcharges for alcohol and Marijuana and the test accuracy. That is why anyone arrested for a DUI offense needs to get legal help immediately, regardless of which substance it was.

    • Turner Kayston

      It’s still disproportionate and unjust, especially per se limits on THC.

      I thought it was well mentioned in the The Journal of Drug Policy and Practice:
      Volume 10, issue 3 – fall 2016:

      Why a 5 ng/ml THC Limit is Bad Public Policy – and the Case for Tandem per se DUID Legislation

      Unfortunately, I cannot link to it from here – but overall, it has some good objective information within (even if it has thing some people don’t agree on); including how the measurement of alcohol impairment are also improper, especially for THC!

      The Canadian Drug Policy Coalition also recently came up with the similar views in their studies and the vast references they provided.

  • Nominalis

    Ethyl alcohol is the only drug that can enter every cell in your body. It gets you thoroughly impaired from head to toe. THC affects specific receptors in your brain so the vast majority of your mind and body isn’t impaired by it. The difference between alcohol and cannabis is the difference between sloshed and sensitive.

    • Turner Kayston

      100% agreed and I have many links to many studies, that back up all the points you’ve given.

      Since I can’t link to any here, you might also be interested in the views of UK Professor, Psychiatrist and NeuroPsychoPharmacologist David Nutt, on youtube or elsewhere.

      He studies the effects of all sorts of drugs on the brain (Cannabis, LSD, psilocybin, ayahuasca DMT, MDMA, you name it), complete with neuroscans in his lectures and alcohol is rated the worst, of all.

      If you google “Drug harms in the UK” and clink on the 3rd or 4th link, the one that links to (/whatwedo/drugharms) it has a video and the famous lancet report… =)

      To quote – page 97 of his book, ISBN: 1906860165:

      “There is no such thing as a safe level of alcohol consumption. Alcohol is a toxin that kills cells and organisms, which is why we use it to preserve food and sterilize needles. Acetaldehyde, produced when the body breaks down alcohol, is even more toxic, and any food or drink contaminated with the amount of acetaldehyde that a unit of alcohol produces would immediately be banned as having an unacceptable health risk.”

      Acetaldehyde (a close relative of formaldehyde) is a poisonous byproduct of alcohol metabolism and is more toxic than alcohol itself.

      Just saying… =)

      • Nominalis

        Thanks. I’ll check out that info. Below is my standard comment on the subject…

        Nobody, including the police, cared about the issue of cannabis and driving until legalization became a looming reality. Then suddenly “cannabis impaired driving” became the cause celebre of the prohibitionists. If cannabis was a causal factor in car crashes this would have been on the radar 5 decades ago.

        • Turner Kayston

          It’s as if they thought all Cannabis consumers were just simply taking the bus before, or something stupid like that.

  • I totally agree with Nominalis because alcohol is a powerful and dangerous drug, and the idea of thinking that marijuana can be compared to alcohol is just ludicrous

  • Wise Pen

    Alcohol is a form of anesthesia,no amount of cannabis can have the same effect.