Is There a Breathalyzer for Marijuana?

If you are pulled over for driving under the influence (DUI) in South Carolina, you can expect to take a series of field sobriety tests on the side of the road, followed by a breathalyzer test at the station – is there a breathalyzer for marijuana, though?

Does SC have any reliable means of testing how stoned a person is, as opposed to how drunk they are?

Are Marijuana Breathalyzers Reliable?

As far as I know, SC police are not using any type of marijuana breathalyzer yet. Other jurisdictions across the country, however, are experimenting with different types of breathalyzers for THC – do they work?

What’s the Difference Between an Alcohol Breathalyzer and a Marijuana Breathalyzer?

An alcohol breathalyzer tests for alcohol on a person’s breath – the amount of alcohol detected on the breath is then multiplied by an arbitrary number (2100) that is supposed to then convert the breath-alcohol content into blood-alcohol content.

It’s not foolproof, and there are many ways the alcohol test can go wrong – the 1/2100 ration is not accurate for many people, for example. The machine has plenty of “moving parts,” and there are many scenarios that can cause a malfunction, including the simulator solution’s temperature and expiration date, whether the mouthpiece is kept clean, whether the subject is chewing gum or candy, whether they have any foreign objects in their mouth like dentures or piercings, whether they burp before the test is given, radio interference… it’s not perfect.

What about marijuana breathalyzers?

Police can order a blood test or urine test to determine the levels of THC that may be in a driver’s system, but those samples must be sent to a lab and the results may not come back for weeks or months. That is why police want an “instant” portable breath test that can tell them just how stoned a person is and whether they are safe to drive…

A Breathalyzer for Marijuana Doesn’t Provide the THC Levels

A breathalyzer for marijuana, however, can’t tell the officer how much marijuana a person has smoked or their level of intoxication. No marijuana breath test claims to be able to give the exact levels of THC a person has in their system.

So far, the tests that are being used nationwide can only tell an officer if THC is present. That’s a problem, because THC can stay in a person’s system for as long as 30 days – is a person DUI if they smoked weed 30 days ago? The day before?

Even cheek swabs – a method being tested by the Massachusetts state police – do not tell what a person’s THC levels are or how their marijuana consumption affects their driving ability…

A test developed in California claims to be able to tell the officer if a person smoked marijuana in the previous few hours – but even that tells the officer nothing about how intoxicated a person is. Arresting a person because they smoked a joint within the past few hours is comparable to arresting a person because they drank a beer within the past few hours – that’s not DUI.

Breathalyzers Can’t Tell an Officer Whether a Person is Intoxicated from Marijuana

What if they smoked marijuana the day before? Odds are, they are no longer stoned, and they are safe to drive – how would the officer know, if the test tells him there is THC present?

What if the driver smoked marijuana just before they got into their car? SC’s DUI laws don’t make it a crime to smoke marijuana and then drive, just like it’s not a crime to drink and then drive – it’s a crime to drink (or smoke) to the point where your faculties to drive are materially and appreciably impaired.

If a marijuana breathalyzer tells an officer there is THC in your system, that tells the officer nothing about your level of impairment…

Should the SC Legislature Set a THC Limit for Marijuana DUIs?

With alcohol, the SC legislature has decided that a blood alcohol content (BAC) of greater than .08 creates a rebuttable inference that a person is driving under the influence. Can’t they do the same thing with marijuana?

Seven states have already set limits for blood THC content (BTC? BTHCC?) – despite agreement among scientists that the levels set by the legislature are meaningless…

“We just don’t know whether or not that means they’re still intoxicated, or impaired or not,” [a chemical engineer at the National Institute of Standards and Technology in Boulder, Colo.] said. “There’s no quantitative measure that could stand up in a court of law.”

First, the existing marijuana breath tests don’t tell an officer the level of THC in the system. But, even if they did, it is impossible to say what a smoker’s level of impairment is based on their THC levels – people who smoke occasionally will have lower levels of THC, people who smoke often will have much higher levels of THC, and different levels of THC affect different people in dramatically different ways.

According to

…the problem is that recent research clearly shows that the levels of marijuana’s active compound, called tetrahydrocannabinol or THC, don’t line up in a straightforward way with how impaired people are, according to the paper, published today (Jan. 25) in the journal Trends in Molecular Medicine.

Some people “can be extremely impaired at 1 nanogram per mililiter [ng/mL], but other people may not have much impairment at all at 5 ng/mL,” said paper co-author Marilyn Huestis, a toxicologist and adjunct professor of epidemiology and public health at the University of Maryland School of Medicine.

How Does Marijuana Use Affect Driving?

No one knows – studies have had mixed results and it is still a controversial topic.

Admittedly, smoking an excessive amount of marijuana will impair a person’s driving similar to alcohol. But, at what point is a person’s driving negatively affected?

A study by the National Institute on Drug Abuse found that subjects were impaired by marijuana use – the question is just how impaired are they and at what level of THC do they become impaired? The study found that subjects began weaving within their lane (not a crime, by the way) at a THC level that is comparable to a BAC level of .08, but they did not leave their lane as the subjects impaired by alcohol did…

And, that THC level was twice the limit set by state legislatures:

The researchers looked at 250 parameters of driving ability, but this paper focused on three in particular: weaving within the lane, the number of times the car left the lane, and the speed of the weaving. While alcohol had an effect on the number of times the car left the lane and the speed of the weaving, marijuana did not. Marijuana did show an increase in weaving. Drivers with blood concentrations of 13.1 ug/L THC, the psychoactive ingredient in cannabis, showed increase weaving that was similar to those with a .08 breath alcohol concentration, the legal limit in most states. For reference, 13.1 ug/L THC is more than twice the 5 ug/L numeric limit in Washington and Colorado.

If the SC legislature decides to set limits on the amount of THC in a person’s blood, or if SC police begin using marijuana breathalyzers on the roadside, rules need to be set that are based on valid science and not myths or uneducated fears about marijuana use.

Marijuana and DUI Defense in Columbia, Lexington, and Myrtle Beach, SC

Lacey Thompson defends clients charged with driving under the influence and drug crimes in Richland County, Lexington County, Horry County, and the surrounding areas.

If you’ve been arrested in SC, call now at 843-444-6122 or email us online to talk with a DUI defense attorney today.

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