Can Breathalyzers Measure Marijuana?

Posted by Lawrence Taylor on February 10th, 2016

I’ve written here in past posts about the difficulties of trying to use a breathalyzer on a driver to determine whether he is under the influence of marijuana.  See Is It Possible to Prove Driving Under the Influence of Drugs?.   As a study authored by Dr. Jim Hedlund, formerly a senior official with the National Highway Traffic Safety Administration, has concluded:.

The relations between a drug’s presence in the body, its concentration, measured in blood, breath, saliva or urine, and its
impairing effects are complex and not understood well. A drug may be present at low levels without any impairing effects. Some
drugs or metabolites may remain in the body for days or weeks, long after any impairment has disappeared (Berning et al., 2015;
GAO, 2015).

In particular, marijuana metabolites can be detected in the body for weeks after use (Berning and Smither, 2014).
On the other hand, concentrations in the body of some drugs decrease rapidly while impairing effects persist. For marijuana,
THC concentrations fall to about 60% of their peak within 15 minutes after the end of smoking and to about 20% of their peak
30 minutes after the end of smoking while impairment lasts for 2 to 4 hours (Kelly-Baker, 2014; Logan, 2014).

In addition, individuals differ in how their bodies absorb and metabolize a drug. In experimental settings, wide ranges of drug
concentrations produce similar levels of impairment in different individuals (Berning et al., 2015). NHTSA’s observation is generally
accepted: “At the current time, specific drug concentration levels cannot be reliably equated with a specific degree of driver
impairment” (Berning et al., 2015). GAO (2015) agrees: “identifying a link between impairment and drug concentrations in the body,
similar to the 0.08 BAC threshold established for alcohol, is complex and, according to officials from the Society of Forensic
Toxicologists, possibly infeasible.”

Will science and profit-hungry corporations ever be able to produce a breath-analyzing device that can accurately and reliably measure the amount of marijuana in a a driver’s blood?  Doubtful, but not for lack of trying.  The following is from a recent edition of Forensic magazine:

“At the same time that marijuana use is growing dramatically, law enforcement has been impeded by the lack of tools to help identify stoned drivers and get them off the road,” according to the company Hound Labs.

Now, the company is claiming they’ve created a technology capable of detecting THC (tetrahydrocannabinol) levels below 500 pg in a breathalyzer test.  According U.S. News & World Report, the technology will be tested early next year in clinical trials.

“Measuring marijuana is not a simple extension of the technology in current alcohol breathalyzers,” according to Hound Labs. “The approach used in an alcohol breathalyzer won’t detect THC molecules in lungs because THC requires a scientific method more than a million times more sensitive than one needed to measure alcohol. Until now, very large, expensive and specialized detection tools were needed to detect THC in breath.”  

The company’s CEO Mike Lynn said the law enforcement version of the product will sell for “well under a thousand dollars,” and the commercial consumer version will be even less, reports the U.S. News & World Report.

If true, this would be quite a break-though.  If true….

  • So far in Colorado a DUI conviction for marijuana requires proof of actual impairment. Seems to me that should be the standard for all cases, whether alcohol or drugs. Current wisdom seems to be that marijuana affects different people differently as to impairment. Can’t the same be said of alcohol? Recently, my 5 foot one 115 lbs. mother in law blew a .13 thirty minutes after half a glass of wine and I (6’-3”, 225lbs) blew a .03 on a full glass (after 30 minutes). She was no more impaired than I was. We were using a pretty expensive and sophisticated portable breathalyzer.

  • DUIBlog

    The standard in California is a Blood Alcohol Concentration of .08 or higher. So in the example of you and your mother in law, she may be convicted and you may be exonerated, regardless of how each of you feel at the moment of driving.

    A driver can also be charged and convicted of a DUI if he or she is driving a motor vehicle while they are “impaired”, and under the influence of alcohol, or drugs, or both. “Impaired Driving” is a subjective standard— it could mean driving too slow, or too fast, or making abrupt turns, or any one of dozens of driving patterns. Sometimes, “impaired driving” can mean you caused a traffic collision.

    “Impaired driving” does not require a driver to be .08; It just requires an officer’s testimony that a driver was driving a motor vehicle in a way that suggests he/she was impaired, plus the presence of drugs or alcohol in any amount.

    To go back to your example with your mother-in-law, you having a BAC of .03 does not automatically exonerate you. It’s certainly helpful to your case that you are under .08, but that’s not the end of the analysis. If you caused a traffic collision and you are only .03, or if you are driving erratically and only .03, you may still be charged (and convicted!) under California law. That is why you must always consult with an experienced DUI attorney if you are ever charged with Driving Under the Influence.