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Marijuana DUI Laws

While marijuana possession and use are now decriminalized under California State law, driving under the influence of marijuana is still a crime. Marijuana DUI cases are being prosecuted frequently in Orange County and the Orange County District Attorney's Office places it's Deputy District Attorneys is a full time DUID assignment, designated specific Prosecutor's in each jurisdiction to handle exclusively DUI drug cases. Because these cases require a special knowledge of toxicology and the changing habits of California drivers, a specialized unit is necessary to prosecute these cases effectively.

The 2019 version of the California Vehicle Code allows for two ways for the prosecutor to file a DUI charge for driving under the influence of marijuana or any other drug. Note it is not a defense if the drug is legal. The crime is based on driving under the influence of the drug. Much like DUI alcohol. While it's legal for anyone over 21 to drink alcohol in the state of California, it's a crime to drive under the influence.

Pursuant to VC 23152(f) It is unlawful for a person who is under the influence of any drug to drive a vehicle. Under VC 23152(g) It is unlawful for a person who is under the combined influence of any alcoholic beverage and drug to drive a vehicle. The California Jury Instruction under CALCRIM 2110 further clarifies that A person is under the influence of an alcoholic beverage and/or drug if as a result of his or her drinking and/or taking a drug, his or her mental or physical abilities are so impaired that he or she is no longer able to drive a vehicle with the caution of a sober person, using ordinary care, under similar circumstances.

The effects of marijuana are not nearly as predictable as alcohol and the existing toxicology is trailing behind the reality of legalization. Much of the research below can be used effectively to defend against a marijuana DUI charge.

Andrea Roth
UC Berkeley School of Law Assistant Professor
The Uneasy Case for MJ as Chemical Impairment
California Law Review
08/01/2015

  • The well acknowledged truth is that there is no known relationship between THC blood levels and increased relative crash risk documented by single car crash or classic case-control studies
  • There is no known relationship between a driver's THC blood level and his level of driving impairment
  • To the extent such studies do exist, they suggest if anything that drivers with THC in their blood are NOT causing a disproporitionate number of fatal crashes
  • Contrast this to alcohol impaired drivers-historical and undeniable statistical correlation in percentage of single car fatalities involving alcohol intoxicated drivers (AKA the Haddon era framework for criminalizing driving at certain level of alcohol impairment)
  • In Haddon's studies-nearly 50% of the drivers killed in single car fatal collisions were .15 or higher BAC. This was originally used to make .15 the limit
  • But looking at 4 studies of MJ involved single car fatal crashes the numbers are in the low single digits and lower than the percentage of drivers that test positive in random testing. Therefore no correlation. If anything MJ use is UNDER represented in single car fatal crashes
  • Brubacher study of crash risk reaches similar conclusions
  • Marijuanas relationship to driving impairment more difficult than alcohol for following reasons

Proximity of use issues

  • cannabis has over 421 chemicals
  • after smoking cannabis, the body breaks down more than 2000 chemicals
  • THC and its metabolites can remain in the body long after the pyschoactive effects have worn off
  • THC itself can remain for hours or even days after consumption
  • 2014 Norway study found THC up to 8 days after use in frequent users (HT Andas et al)
  • Metabolites can linger even longer, days, weeks, or even months for chronic users (citation 289) NOTING half life of THC for non users is 1.3 days, for chronic users 5-13 days

Even Huestis in her article on "models for the prediction of time of marijuana exposure from plasma concentrations" says heavy users (frequent smokers) residual levels of THC have been measured for extended periods of time after cessation of drug use. Citing to study called "prolonged half life of THC in plasma of chronic marijuana users" by E Johansonn

  • 2014-Odell article-Residual cannibis levels in blood following heavy cannabis use
  • 2015-Extended plasma cannabinoid exrection in chronic frequent cannabis users

In sum, marijuana's unpredictable qualities render nearly impossible any determination from THC blood levels alone whether a person is actually under the influence of marijuana at the time of driving or has simply ingested marijuana in the somewhat recent past.

Dose related issues

Alcohol BAC is highly correlated to the level of alcohol intoxication in the brain and therefore high correlation to psychoactive effects. Predicable and uniform because alcohol is fat and water soluable, only effective at high concentrations and equilibriates between brain, blood and other tissue. Because alcohol is soluble in water, its is also soluble in BLOOD. This is why it moves easily into the blood and is easily measured in the blood. Pharmacodynamics of alcohol are well understood (how it works)

MJ is different, more complex more disconnected to its levels in bodily fluids. MJ is highly fat soluble but BARELY soluble in water, therefore unlike alcohol is does not reach a uniform concentration throughout the body. Therefore the level of THC in the brain or the psychoactive effect in NOT predictable from the amount in the blood. Hydroxy has SOME psychoactive effects but much smaller than THC itself and Hydroxy's psychoactive effects on the brain is unconnected to the level in bodily fluids. Carboxy has NO pyshoactive effects. Scientists are NOT in agreement on exactly why and how THC affects the brain. MJs unpredictable properties render nearly impossible any inference about the likely psychoactive effect on the brain of a specific THC level.

Impairment of Ability to Drive Issues

Alcohol is simply a different drug and BAC corresponds so predictably to proximity of use, brain concentration and level of type of psychoactive effect-this all makes the study BACs effects on driving easy to study and predict. Alcohol qualities, the non invasiveness of breath testing, and legality give us more data to work with.

1983-Natiional institute on drug abuse conference discussed using DUI alcohol model for DUI drugs and concluded that "ethanol is an unusually good model for studying the effects of a drug on driving performance" when compared to other drugs

2002-The Walsh Group "iterpreting the meaning of either drug or metabolite concentration is a single biological specific with reference to impaired driver performance is therefore an extremely difficult task fora scientist" cite 310

2005 K. Papafotiou Relationship between performance on SFST, driving performance, and level of THC in the blood said "The level of THC in the blood does NOT provide an accurate an reliable indicator of whether driving performance is impaired"

2005-Franjo Grottenhermen "Developing science based per-se limits for driving under the influence of cannabis". Impairment effects of a strong does of 15-20 mg of THC after about 3 hours are comparable to a BAC of about .03. Also hypothesized that DRUNK drivers tend to underestimate risk and therefore drive poorly, THC intoxicated drivers overcompensate for a known risk.

2010-NHTSA report on drugged driving conceded that it the presumptive and per se laws for alcohol DUI laws were only the result of the solid evidence of increased crash risk with higher BACs, something we don't see with MJ statistics

2012-Gary Reisfeld, a physician, wrote in Journal of Analytical Toxicology finding drug concentrations analogous to the .08 BAC level in terms of indicating unsafe levels of intoxication is "unachievable". Ability to determine impairment on numerical thresholds in a mirage. Only way to enforce is zero tolerance or per se law, although arbitrary, its only way to make it enforceable. IF we insist on showing impairment, we can't do it.

2014-2 NHTSA researchers said "current knowledge about the effects of drugs other than alcohol on driving performance is insufficienct to make judgments about connections between drug use, driving performance and crash risk"

May 2019 forum at UCI as reported by OC register Huesis said "there's not a good scientific case right now for per se limits"

"Signs of cannabis use can turn in blood tests LONG AFTER the mind altering effects have worn off"

MJ stored in fat cells-factors that influence how quicky metabolize include tolerance ,ROA, drugs potency, and gender

Huestis said "THC levels can go UP over time even without ingesting any more MJ if the people are physically active"

Chronic users can show high levels of THC in blood even when not impaired

NHTSA website cannibis/mairjuana fact sheet-"it is difficult to establish a relationship between a persons TCH concentration and performance impairing effects