How Should California Test for Marijuana DUIs?

by on April 30, 2014 · 6 comments

in California, Civil Rights, Culture, Environment, Health, History

Med MJ joint in carEditor:  A bill in the California legislation that would have created per se limits on driving under the influence of specified drugs – like marijuana – based on blood tests even absent other evidence of impairment, AB 2500, just failed in the Public Safety Committee.

More bills like this are expected. So, this may be a good time to see what a law enforcement group in favor of marijuana legalization has to say on marijuana DUIs.


By Law Enforcement Against Prohibition

Marijuana DUIs

  • Unlike alcohol, THC can stay in the bloodstream for days or weeks. We must find a way to accurately measure the impairment of a driver if we’re going to fairly charge them with a crime. Currently, officers in every state but West Virginia are being trained to become drug recognition experts who can recognize the signs of drug impairment and make arrests for drugged driving offenses (4) Blood tests should be no substitute for good police work.
  • The National Highway Traffic Safety Administration says “It is difficult to establish a relationship between a person’s THC blood or plasma concentration and performance impairing effects.” and “It is inadvisable to try and predict effects based on blood THC concentrations alone, and currently impossible to predict specific effects based on THC-COOH concentrations.” (8)
  • A study published by the Journal of Law & Economics found that adoption of medical marijuana laws is associated with a decline in traffic fatalities(1)
  • DUI fatalities in both Colorado and Washington slightly decreased after legalization went into effect. 2013 data in Washington is still preliminary, but for the first three quarters there were only 317 fatalities; for the first three quarters of 2012, before legalization went into effect, there were 327. Similarly, in Colorado in 2012 there were 434 fatalities; preliminary data for 2013 shows there were only 424. (6)
  • The study showing an increase in number of DUI drivers with THC in their blood that opponents like to cite was based on six states (3), three of which didn’t have medical marijuana/legalization/decriminalization laws during the study, so the increase is not a product of changing marijuana laws. The three that did have medical marijuana laws – California, Hawaii and Rhode Island – saw sharp decreases in traffic fatalities between enactment of their medical marijuana laws and the end of the study period. Fatalities fell 31%, 14% and 21%, respectively. (2)
  • Marijuana seems to be a substitute for alcohol – medical marijuana laws are associated with decreases in the probability of having consumed alcohol in the past month, binge drinking, and the number of drinks consumed. (1)
  • Traffic fatalities may be decreasing in association with this this substitution effect and the fact that most people drink alcohol on weekends outside of the home (parties, bars, restaurants, etc) and are more inclined to drive after having consumed… whereas most marijuana is consumed in the home or other private locations, meaning there is less reason/necessity to drive after consumption (1)
  • Someone who uses marijuana very little or rarely will be more impaired and make more mistakes than someone who smokes more and more frequently. (1) This ties into the 5ng THC/ml of blood limit some states have enacted because it’s very possible that someone with a higher ng count is actually less likely to cause an accident.
  • While alcohol causes an increase in traffic fatalities, it remains legal because, as we found out in the 1920s, regulation and control is a better policy than prohibition. But we also promote responsible policies to prevent driving while intoxicated and punish those who break the laws. We need a similar policy in place for marijuana.






5. 5. (Download report)

6. 6.



Law Enforcement Against Prohibition is a 501(c)3 nonprofit of law enforcement officials opposed to the war on drugs.

For interviews, please contact Darby Beck at or 415.823.5496.

{ 6 comments… read them below or add one }

jerry garcia April 30, 2014 at 12:06 pm

find me any proof of the fact that you drive worse while under the influence of marijuana. In 1961 california did a highly ignorned study that proved people drove better while stoned. So until the federal government stops putting bans on this kind of testing at universities and other places that this testing could happen we will never really know, they can make up whatever they want and keep us in their private jails while fooling us into thinking marijuana is or can be legalized, when in fact even in legal states, it will become more illegalized through BS laws like this that don’t proove how high you really are. Gotta keep those jails full, we have the most people jailed in the world and we call ourselves the land of the free. free my ass, we are under constant war with our police who beat and kill us and our government who spies on us and drones children to death everyday.


CC May 1, 2014 at 9:07 am

To be honest, I drive worse when I’m really stoned. It’s been a few years since I’ve done that but depending on how much you’ve smoked, similar to drinking, matters.

Sure you can smoke a little and drive and be fine. But some people smoke so much they’re inebriated.


mjt April 30, 2014 at 1:24 pm

Stop driving, whether a user or not. Design your life away from the car.
Save a bundle of money, have less stress, and be safer. Cars suck!

The last time I put gas in my car was in July.


Krymsun May 6, 2014 at 7:57 am

Why does most everyone jump to the automatic, knee-jerk, and FALSE assumption that cannabis impairs drivers much the same as does alcohol? Why let uninformed opinions be the basis of new laws? It took me very little time to do a search, and find actual scientific studies which indicate just how incorrect such an assumption is. Examples follow.

Studies Show Marijuana Consumption Not Associated With Dangerous Driving, May Lead to Safer Drivers
Anyone who consumes cannabis on a regular basis knows that it doesn’t make you a dangerous driver. Many people find that it makes them a safer, more focused driver; one that’s more aware of their surroundings and the dangers associated with controlling tons of gasoline-filled metal. Not only has this been an anecdotal truth for as long as cars and cannabis have been paired, science has also been clear that consuming marijuana doesn’t make you a dangerous driver, and may make some people safer drivers. More research is needed, but it’s hard to deny that of the research we have, marijuana hasn’t been found to increase a person’s risk of an accident. To back this claim up, here’s a list of studies and research conducted on this very topic, some of which were funded by national governments in hopes of different results.

Marijuana and Driving: A Review of the Scientific Evidence
“Marijuana has a measurable yet relatively mild effect on psychomotor skills, yet it does not appear to play a significant role in vehicle crashes, particularly when compared to alcohol. Below is a summary of some of the existing data.”

The incidence and role of drugs in fatally injured drivers
“There was no indication that cannabis by itself was a cause of fatal crashes.”
REFERENCE: Washington, DC: US Department of Transportation, National Highway Traffic Safety Administration,
Report No. DOT HS 808 065, K. Terhune. 1992.

Marijuana’s effects on actual driving performance
“Evidence from the present and previous studies strongly suggests that alcohol encourages risky driving whereas THC encourages greater caution. .. Drivers under the influence of marijuana retain insight in their performance and will compensate when they can, for example, by slowing down or increasing effort. As a consequence, THC’s adverse effects on driving performance appear relatively small.”
REFERENCE: University of Adelaide study, 1995

Role of cannabis in motor vehicle crashes
“There is no evidence that consumption of cannabis alone increases the risk of culpability for traffic crash fatalities or injuries for which hospitalization occurs, and may reduce those risks.. The more cautious behavior of subjects who have received marijuana decreases the impact of the drug on performance, whereas the opposite holds true for alcohol.”
REFERENCE: Marijuana: On-Road and Driving-Simulator Studies; Epidemiologic Reviews 21: 222-232, A. Smiley. 1999.

“Both simulation and road trials generally find that driving behaviour shortly after consumption of larger doses of cannabis results in (i) a more cautious driving style; (ii) increased variability in lane position (and headway); and (iii) longer decision times. Whereas these results indicate a ‘change’ from normal conditions, they do not necessarily reflect ‘impairment’ in terms of performance effectiveness since few studies report increased accident risk.”
REFERENCE: UK Department of Environment, Transport and the Regions (Road Safety Division). 2000.

Cannabis And Cannabinoids – Pharmacology, Toxicology And Therapy
“At the present time, the evidence to suggest an involvement of cannabis in road crashes is scientifically unproven”.
REFERENCE: G. Chesher and M. Longo. 2002.,Toxicology%20And%20Therapy.pdf

Cannabis: Our position for a Canadian Public Policy
“Cannabis alone, particularly in low doses, has little effect on the skills involved in automobile driving. Cannabis leads to a more cautious style of driving. However it has a negative impact on decision time and trajectory. This in itself does not mean that drivers under the influence of cannabis represent a traffic safety risk”
REFERENCE: Canadian Senate Special Committee on Illegal Drugs. 2002.

“The evidence to suggest an involvement of cannabis in road crashes is scientifically unproven.”
REFERENCE: Cannabis and Cannabinoids: Pharmacology, Toxicology, and Therapeutic Potential, 2002
Cannabis and Cannabinoids: Pharmacology, Toxicology, and Therapeutic Potential, edited by Franjo Grotenhermen, MD and Ethan Russo, MD (Haworth Press 2002).,Toxicology%20And%20Therapy.pdf

The Prevalence of Drug Use in Drivers, and Characteristics of the Drug-Positive Group
“There was a clear relationship between alcohol and culpability. In contrast, there was no significant increase in culpability for cannabinoids alone.”
REFERENCE: Accident Analysis and Prevention 32(5): 613-622. Longo, MC; Hunter, CE; Lokan, RJ; White, JM; and White, MA. (2000a).

The Effect Of Cannabis Compared With Alcohol On Driving
“Although cognitive studies suggest that cannabis use may lead to unsafe driving, experimental studies have suggested that it can have the opposite effect.” U.S. National Library of Medicine, 2009

Why Medical Marijuana Laws Reduce Traffic Deaths
“No differences were found during the baseline driving segment (and the) collision avoidance scenarios,”
REFERENCE: Research published in the Journal of Psychoactive Drugs, 2010

Top 10 Reasons Marijuana Users Are Safer Drivers
“20 years of study has concluded that marijuana smokers may actually have fewer accidents than other drivers.”

Risk of severe driver injury by driving with psychoactive substances
“The study found that those with a blood alcohol level of 0.12% were over 30 times more likely to get into a serious accident than someone who’s consumed any amount of cannabis. .. The least risky drug seemed to be cannabis and benzodiazepines and Z-drugs.”
REFERENCE: Accident Analysis & Prevention; Volume 59, October 2013, Pages 346–356

Cannabis: Summary Report
“Cannabis alone, particularly in low doses, has little effect on the skills involved in automobile driving.”
REFERENCE: Canadian Senate Special Committee on Illegal Drugs,Toxicology%20And%20Therapy.pdf

Acute cannabis consumption and motor vehicle collision risk
“There is no evidence that consumption of cannabis alone increases the risk of culpability for traffic crash fatalities or injuries for which hospitalization occurs, and may reduce those risks.”
REFERENCE: British Medical Journal, 1999; M. Bates and T. Blakely

Marijuana-DUI Case Tossed by Arizona Supreme Court in Metabolite Ruling
“Because the legislature intended to prevent impaired driving, we hold that the ‘metabolite’ reference in [the law] is limited to any of a proscribed substance’s metabolites that are capable of causing impairment . . . Drivers cannot be convicted of the . . . offense based merely on the presence of a non-impairing metabolite that may reflect the prior usage of marijuana.”


Patricia February 14, 2019 at 10:17 pm

It’s a fact, 70% of Americans smoke weed while driving, but adults are more responsible and show more control on the road. Young people, unfortunately, don’t pay attention to the road, so more accidents are reported with teens involved in car crashes. Check the stats:


Steven Bradley March 27, 2019 at 5:56 am

Interesting blog. I have enjoyed reading them. I will come to look for new update. Keep up the very good work.


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