If a law enforcement officer pulls you over after suspecting that you’re driving while drunk, they can administer a breathalyzer test to estimate your blood alcohol content (BAC). It’s a relatively straightforward process since states and countries tend to agree on what BAC constitutes driving under the influence.

Companies and researchers are also creating breathalyzers that detect marijuana. The concept might sound useful to some people because it could keep impaired drivers off the road — but it’s not as straightforward as it seems.

Measuring Recent Usage, Not Amounts

Hound Labs Breathalyzer Marijuana


A company called Hound Labs is one of the leading brands offering this new kind of breathalyzer. Its model seems particularly handy because it checks for both alcohol and marijuana. Moreover, it gives results regardless of whether a person smoked marijuana or consumed an edible.

The main issue with the product is that it can detect usage but doesn’t give precise amounts. It would register marijuana in your breath no matter how much you smoked or ate within the last couple of hours. That’s problematic because it groups everyone into one of two categories — people who have used and people who haven’t.

Why should people get the same treatment whether they’ve smoked continually for two hours or took a nibble of their friend’s pot brownie during that span? That’s certainly not the case with our alcohol breathalyzers.

Relying on a breathalyzer to determine whether an individual used marijuana could also penalize someone who uses medical marijuana. Such an option is not legal everywhere, but in the places that permit it, people have several options to consume marijuana for relief from their health issues. They can smoke, vaporize or ingest it or apply it topically.

It should be easy for us to see, then, that in many instances, it may be too restrictive for law enforcement officials to crack down on a person for merely using marijuana. If police forces start depending on these breathalyzers, people who have the right to use marijuana may start feeling fearful of being unfairly targeted by law enforcement.

Too Much Inconsistency for Widespread Usage

Candian Weed

Substantial variations exist concerning whether people can use marijuana in certain places, and if so, how. In the U.S., some states allow it only for medical use, while others give the go-ahead for recreational usage as well. Others have so far only decriminalized it, which means users don’t get jail time if caught but may pay fines. Some states still ban use altogether, but progress is even taking place in those places, as legislators consider whether to permit marijuana use for specific reasons, such as medicinally.

Aside from the lack of agreement regarding where people can use marijuana and for what reasons, perhaps the next most significant inconsistency concerns amount. For example, in Colorado, prosecution is legal if people have at least five nanograms of tetrahydrocannabinol (THC) per milliliter of blood. But doctors say it’s difficult to gauge how much marijuana causes impairment. That problem creates a gigantic grey area that will persist until further research helps provide reliability.

A few states prohibit people from driving if they have any amount of THC in their blood. A breathalyzer could work in those places, but individuals rightfully point out that such a law overly restricts those who use the substance medically. These differences in regulations between states complicate things for individuals who travel across state lines frequently.

A Prototype That Measures THC

Nanotechnology breathalyzer

It should be clear why only measuring whether a person used marijuana creates too many complications. Researchers at the University of Pittsburgh say they’ve developed a breathalyzer that goes further and quantifies the amount of THC in the blood. The gadget uses machine learning and can detect levels of marijuana even if a person has used other substances along with it.

The researchers confirmed that those using their breathalyzer still must agree on what measurement equals driving under the influence. That said, they anticipate manufacturing their machine for widespread use soon and say it could help provide more details about the extent of a person’s usage.

Not Enough Agreement

Weed Breathalyzer

Some people who support using a breathalyzer to test for marijuana say they’re in favor of it because those who choose to use it must be responsible about their usage before they get behind the wheel, just as those who drink alcohol should be. That makes sense, but for now, the two main issues that could significantly impact the rollout and widespread adoption of marijuana breathalyzers are the lack of a national standard to say what equals driving high and scientists’ uncertainty about how much marijuana impacts a person’s ability to drive.

Until the different factors get clarified, using marijuana breathalyzer technology could promote unnecessary punishment or penalties that law enforcement officers dole out arbitrarily due to the existing grey areas. These devices could give the police some answers they can’t quickly get now, but other questions must be handled before the breathalyzer results can be feasible.

Kate Harveston
Kate Harveston is a freelance writer from Pennsylvania. She mainly writes about legal issues and the political realm, but her work has covered a wide range of topics. If you like her writing, you can follow her on Twitter or subscribe to her blog,