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Driving Under the Influence of Marijuana: Weed Laws


It’s been almost a year since weed was legalized in California, but a lot of questions remain, particularly with regards to marijuana and driving.

How much do you have to worry about stoned drivers?

And if you are a marijuana user, what precautions should you take to avoid getting a marijuana DUI?

Unfortunately, there’s no 100% clear answer to the question of how much more dangerous our roads will become. But if you familiarize yourself with the law, it is relatively easy to avoid being cited for driving under the influence of marijuana. In this article, we shall go over that, as well as some of the other problems related to marijuana legalization and driving.


gavel and week leaf

The Problem of Marijuana DUI

Most of us, by now, are aware of the grave dangers associated with driving drunk. Fewer are aware of the dangers of driving under the influence of marijuana, but this is a very serious problem in its own right.

How much of a problem?

Precise statistics can be difficult to come by, for reasons we’ll explain in more detail below. But the dangers of driving high are clear. Thousands of Americans are killed, and tens of thousands more injured, every year, in DUI accidents involving drugged drivers, and one of the most common substances abused in these accidents is marijuana.

Of course, people were driving under the influence of marijuana long before it was legalized. The drug was still used illegally by many Americans; it is estimated that half of all American adults have tried marijuana at some point, and more than 54 million use it regularly. Medical marijuana has also been legal since 1996.

So, high driving has long been a problem, and police officers already have some familiarity with it. However, the passage of Prop 64 changes the equation. It will likely force the California Highway Patrol and other authorities to address the problem more thoroughly than they have in the past.

Part of this is merely a matter of social perception. When marijuana was still illegal, everyone who used it was a “criminal;” although this designation included millions of otherwise law-abiding Americans, it cast the use of marijuana firmly into the category of deviant behavior.

Now, society and the law will have to readjust their attitudes, and recognize the use of marijuana as socially acceptable behavior while maintaining the perception of driving while under the influence of marijuana as deviant behavior.

This will be a difficult path to walk, and it will likely be some time before authorities in the state of California will be able to establish the proper balance.

Bloodshot eye from smoking weed

What Are the Effects of Marijuana on Driving?

You might think this is a simple and straightforward question, but it isn’t.

Just about everyone agrees that marijuana has some effect on driving, but it’s not quite clear how much.

If you ask some people who have driven high, they may tell you that they can drive just as well while under the influence of marijuana as they do while sober. A few even seem to believe that being high improves their driving! However, many critics of marijuana legalization claim that driving while high is just as bad as drunk driving, if not worse.

The truth, so far as it can be established, is probably somewhere between these two extremes.

First of all, it is virtually certain that marijuana does impair driving, at least to some degree. However, researchers have been unable to establish a link between marijuana and reckless driving that is as strong or certain as the link between alcohol and reckless driving.

We know that marijuana use impairs many of the functions necessary for driving. It decreases reaction time, increases weaving, and impairs the user’s eye tracking abilities. All of these decreases in function are common between high and drunk drivers, although the precise effects of the two substances differ slightly.

Like alcohol, marijuana use also impairs speed and following distance. However, in these areas its effects are the opposite of those of alcohol. While drunk drivers tend to speed and follow cars in front too closely, high drivers tend to drive more slowly and leave a greater following distance.

Just how many accidents do high drivers cause? Here, too, it’s hard to find a number that is 100% reliable.

One reason for this is because not everyone who had marijuana in their system when an accident occurred was intoxicated. As we discuss in more detail below, marijuana presence in the bloodstream does not correlate quite as closely with actual impairment as alcohol does.

In addition, groups which are most likely to smoke marijuana, including young people, men, and those prone to taking risks, are already the groups which are most likely to get in car accidents, regardless of DUI status.

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When you control for these factors, the number of accidents that can be attributed to marijuana often decreases, and it’s hard to say how many accidents are caused by high driving and how many are caused by a tendency towards reckless behavior (which may also lead to a greater likelihood of using marijuana or other drugs).

A recent meta-analysis found some illuminating results. For one, there is more variance in impairment among high drivers than drunk drivers. This is because marijuana, unlike alcohol, has its greatest impairing effects on complex tasks that require conscious control, and so high drivers are more likely than drunk drivers to be able to correct for their own impairment.

Not only that, but high drivers tend to be more aware of their own impairment, which makes them less likely to get behind the wheel in the first place. This is different from drunk drivers, who, if anything, tend to become overconfident in their abilities.

Of course, the risk of accident goes up if the user has both marijuana and alcohol in their system. The two substances can play off each other; marijuana makes alcohol last longer, and alcohol increases the absorption of marijuana into the body. In accidents where the driver tests positive for both marijuana and alcohol, it can be extremely difficult to tell how much each substance contributed to the accident.

That’s the long and short of it. Essentially, we don’t know precisely how much marijuana affects driving, although we can be certain that it has some effect. It will likely take a lot more research before scientists can come to any sort of consensus.

That said, driving while high is never a good idea. Even if the effects of marijuana on driving are not as bad as those of alcohol, you still shouldn’t operate a vehicle while under the influence. The only safe level of impairment is zero.

Marijuana may now be legal for adult citizens to use, but this freedom comes with a duty to use it responsibly, just as you would drink alcohol responsibly. All sides in the debate, including pro-legalization activists, agree that marijuana users should never drive high, both for their own sake and that of the other drivers and passengers who share the road with them.

The pro-legalization National Organization for the Reform of Marijuana Laws (NORML), for instance, says in its Principles of Responsible Cannabis Use that “The responsible cannabis consumer does not operate a motor vehicle or other dangerous machinery while impaired by cannabis, nor (like other responsible citizens) while impaired by any other substance or condition, including some medicines and fatigue.”

Marijuana use is a personal choice, but we strongly encourage everyone to abide by this principle.

Does Legalization Increase Rates of High Driving?

Once again, the precise numbers are hard to come by.

Marijuana has already been legalized in a few states, but it is difficult to tell how many accidents in these states have been caused by high drivers, and whether the numbers have increased since legalization.

The results of research in these states are often conflicting. Some studies have found that collisions related to high driving have gone up, while others find that there has been little to no change.

Even though marijuana was illegal until recently, driving under the influence is nothing new. Will legalization have some impact on this, perhaps by encouraging more first-time users to try the drug, or by inadvertently sending the message that it’s okay to smoke and drive?

It’s difficult to say.

What Does the Law Say About Driving High?

Driving under the influence of marijuana is already illegal in California, and has been since long before the passage of Prop 64.

The law prohibiting drunk driving, which can be found in California Vehicle Code (CVC) 23152, also applies to drugged driving. The penalties for driving high, like those for driving drunk, are severe, and include fines, imprisonment, and suspension of the offending driver’s license.

This law won’t be repealed anytime soon; DUI marijuana will remain on the books in California. But the precise standards which the police use to detect high drivers are liable to change at some point in the future.

How High Is Too High to Drive?

It is relatively easy to tell if a driver is under the influence of alcohol. The officer will typically make their first judgment based on the driver’s appearance, and then, if they suspect that the driver may be drunk, give them a series of field sobriety tests and possibly a breathalyzer or blood test.

With marijuana, it’s a bit more difficult. There are a couple reasons for this.

For one, unlike with alcohol, there is no reliable breathalyzer for marijuana. There have been a few prototypes developed, and even put into use in some jurisdictions, but a true marijuana breathalyzer remains elusive.

For another, marijuana intoxication is simply much harder to measure than alcohol intoxication. That is because tetrahydrocannabinol, or THC, the psychoactive ingredient in marijuana, does not correlate as closely with actual impairment as alcohol does.

With alcohol, one can be fairly certain that a driver with a certain level of alcohol in the bloodstream will be experiencing a certain level of impairment. That is why the level of blood alcohol content (BAC) needed to determine drunk driving, 0.08%, is relatively non-controversial, and is uniform throughout all 50 states.

It is less certain that a driver with a particular level of THC in the bloodstream will be experiencing a particular level of impairment. This is partly because THC dissolves into the body’s fat, rather than the bloodstream, so the amount in the blood does not correspond to intoxication quite as closely.

If an individual uses marijuana frequently, then THC will likely remain in their bloodstream for days or weeks after their last usage, because it will have been stored in their body fat for all that time.

Meanwhile, another person who is very impaired might have hardly any THC in their blood, for instance, if they ate marijuana rather than smoking it. Vaping can also complicate the issue, and different strains of marijuana can have vastly different effects.

For all these reasons, it is difficult to determine impairment by blood THC content alone. Still, some states which have legalized marijuana do take this approach when determining whether a driver is too high to drive.

Washington and Colorado, for instance, both draw the line for THC at 5 nanograms per milliliter of blood. These limits, which are derived from those established by some European countries (where marijuana has been legal for longer than in the United States), have their supporters, but they also have their detractors.

5 nanograms of THC per milliliter of blood could mean very different things for different people.

And there’s another complication: blood samples are often not drawn until several hours after a car accident, allowing the THC levels in a guilty driver’s blood to go down.Click To Tweet

Partly because of these reasons, California does not use this method. Instead, California has implemented a somewhat fuzzier standard for determining whether a driver is too high to drive.

Current California law simply says that anyone who is “under the influence” of marijuana or other drugs can be charged with DUI. What does it mean to be “under the influence”? The law doesn’t explicitly say.

However, according to California Jury Instructions — Criminal (CALJIC) 16.831, a person is considered “under the influence” if they lacked the “ability to drive with the caution characteristic of a sober person of ordinary prudence under the same or similar circumstances.”

Because there are no hard numbers involved in this standard, it’s largely up to the prosecutors and jury in a specific case to determine whether the driver was impaired, but ultimately DUI marijuana rests on a standard that’s largely based in common sense.

If you have recently used marijuana and you believe that it may have impaired your ability to drive as you would ordinarily be able to, then don’t get behind the wheel. Simple as that.
Police officer performing sobriety test

How Do Police Detect High Drivers?

First, the police officer will typically look for clues that you are under the influence of marijuana.

If you have marijuana on you, this is a big red flag. The officers might also have reason to suspect you of driving high if they think you smell like marijuana, or if you are acting intoxicated. Reckless driving may also be a tip-off.

Once the officers have reason to suspect that you may be high, they will perform a series of field sobriety tests on you. These tests are similar to the field sobriety tests for alcohol, although not identical.

Typically, the suspected driver is asked to track the officer’s finger with their eyes, to walk a certain number of steps and then turn around, and to stand on one leg for a certain count. These tests are not 100% effective in determining whether you are intoxicated, but they carry strong sway in court.

Finally, the officers will use a Drug Recognition Expert to detect any overt physical symptoms of intoxication. If those symptoms are present, then they may perform a chemical test on you, most often a blood test, although urine, saliva, and breath may also be tested.

As mentioned above, California has no specific numerical threshold for impairment, so the results of the physical test will be used in concert with other evidence (including reckless driving, physical symptoms, and the results of failed field sobriety tests) to argue that you were driving impaired at the time.

Can I Drive With Marijuana in the Car?

Obviously, you can’t smoke marijuana while driving, or immediately before driving. But what about merely transporting marijuana, with no intention to smoke it until after you have stopped driving?

If you drive with an open container of alcohol in your vehicle, this will get you a ticket in California (and most other states). But when it comes to marijuana, the standards get a little more complicated.

Under California Vehicle Code 23222, drivers are prevented from transporting marijuana, unless they have a medical license. However, this is only an infraction, much like driving with an open container of alcohol.

Furthermore, there is an exception made for marijuana purchases which are authorized by law. Previously, this only included medical patients, but as of the passage of Prop 64, it also includes anyone who possesses quantities of marijuana that are permitted by Prop 64.

Of course, this does not apply to marijuana that falls outside the limits of Prop 64, including that which is possessed by people under 21 or people with more than one ounce. Nor does it apply to open containers of marijuana.

If you have opened the container of marijuana, then this means the same thing as an open container of alcohol: it signals an intent to use the substance. So keep the container closed at all times, and follow the same rules that you would with a bottle of alcohol.

Recently, Governor Brown also signed into law SB 65, which prevents not only drivers, but also passengers from using marijuana while in a vehicle. (The updated rules can be found in California Vehicle Code 23220-23221.) So make sure that your passengers aren’t up to anything!


Now that Prop 64 has passed, there will likely be some further shifts in the legal attitude towards marijuana over the next few years. Will these shifts involve a change in the standards that define marijuana DUI?

Only time will tell, but it is likely that at some point in the future, legal experts will develop a standard that can be used across the board and adopted by every state in the union, just as the standard for alcohol was.

Part of this may come about as a result of Prop 64 itself. The law will place a tax on all legally sold marijuana, and this tax revenue will go to a variety of costs.

Included in these costs are $3 million every year until 2022 (for a total of $15 million) that will be given to the California Highway Patrol, so that it can establish a clearer set of protocols for detecting drivers who are under the influence of marijuana.

In addition, as much as $125 million will be given in grants to law enforcement agencies, to help train officers to spot DUI drivers.

It is worth remembering, however, that even if marijuana has been legalized by the state of California, it is still illegal at the federal level, under the Controlled Substance Act of 1970. This is not likely to change anytime soon. So if you are in possession of marijuana and are dealing with federal authorities, you will likely get a very different result from that which you would get if you deal with state authorities.

Because of the lack of standardization at the federal level, it will likely be a long time before there are standards for marijuana DUI enforcement that are recognized nationwide… unless, of course, the states take it upon themselves to fill the gap that the federal government has left open.

A highly regarded and well-respected trial lawyer, author and speaker, Reza Torkzadeh is the founder and managing attorney of TorkLaw – a premier plaintiff’s personal injury law firm specializing in complex catastrophic injury and wrongful death cases.

Reza’s performance in and out of the courtroom has earned him several of the industry’s top awards and professional recognitions, and a reputation as an elite litigator. He has earned millions in settlements, verdicts, and judgments for his clients.

If you would like a free consultation, please contact us today.