In recent years, GLP-1 medications like Ozempic® (semaglutide), Wegovy®, Mounjaro® (tirzepatide), and Saxenda® (liraglutide) have become household names. They’re prescribed for diabetes management and, increasingly, for weight loss.
But as their use has exploded, another trend has emerged in the DWI defense world: odd, unexplained breath test readings — even in people who swear they have had little or no alcohol! In some cases, the numbers have puzzled not only drivers but even the officers operating the breath machines.
This isn’t the first time we’ve written about “interfering substances” in breath alcohol testing, but the rise of these medications demands a closer look.
The Science: Ketosis and Interfering Chemicals
These drugs are GLP-1 receptor agonists, which mimic a natural hormone and often push the body into ketosis. This is the same fat-burning metabolic state seen in low-carb or fasting diets.
In ketosis, the body produces ketones, including acetone, which can then be converted into isopropanol (a toxic alcohol not fit for consumption).
Here’s the problem: most breath test devices can’t tell the difference between ethanol (drinking alcohol) and certain other alcohols or hydrocarbons. In particular, infrared spectroscopy (the method of analyzing Minnesota breath tests) and fuel cells used in many handheld roadside tests and ignition interlock devices may register acetone or isopropanol as if it were ethyl alcohol, artificially inflating the result.
Studies and real-world case reports have shown:
- Breath test machines can overreport breath alcohol concentration when ketones or isopropanol are present.
- Fasting or ketogenic states can produce breath acetone levels high enough to mimic or add to a true BAC.
- Partition ratio differences between ethanol, isopropanol, and acetone can cause exaggerated readings.
The Minnesota Bureau of Criminal Apprehension (BCA), the Minnesota crime lab, has conceded that individuals who fast, diet, or are highly exercised fall into the same category as those on ketogenic regimens when it comes to producing ketones and potentially interfering with breath alcohol results.
Why This Matters in DWI Defense
For individuals on these medications, whether for diabetes or weight loss, the risk of misleading breath test results is real.
A driver could:
- Exhibit physical signs that officers associate with intoxication (slurred speech, confusion, flushed skin, fruity breath odor) due to hypoglycemia or ketosis, not alcohol.
- Produce a false positive BrAC reading from ketones and isopropanol, even with zero ethanol in their system.
- See their results inflated by 0.05 to 0.10 or more because of interfering substances — enough to push them over the legal limit.
Our Continuing Education Efforts
In June, Chuck Ramsay presented to the Minnesota criminal defense bar on “Refusal By Conduct Defenses and Mouth Alcohol Detection.”
As we always do, we included materials designed to help attorneys representing clients charged with DWI, practical, ready-to-use tools that can make a real difference in case preparation.
Among those materials was our Suggested Medical Questionnaire for Clients, which asks for detailed information about medications. One specific section now addresses GLP-1 drugs like semaglutide, liraglutide, and tirzepatide.
Asking the Right Questions Early
One of the simplest and most important steps we take is to identify potential interfering substances before we start building the defense strategy.
That’s why our client questionnaire now includes:
- GLP-1 Medications (Trulicity, Ozempic, Wegovy, Mounjaro, Zepbound, etc.):
Are you currently taking or have you recently taken any GLP-1 receptor agonist medications (such as Trulicity, Ozempic, Wegovy, Mounjaro, Zepbound, or similar)?
☐ Yes ☐ No
If yes, please list:
(These medications may place the body in a fasted state and increase the production of acetone, a byproduct of fat metabolism.)
By capturing this information at intake, we can identify cases where a breath test result may have been influenced by ketosis-related interferents, such as acetone or isopropanol, and begin challenging the reliability of the number before the prosecution builds their narrative.
PRO-TIP FOR DEFENSE LAWYERS:
With the proliferation of GLP-1 drugs, defense attorneys should:
- Ask clients about use of semaglutide, liraglutide, tirzepatide, or other GLP-1 medications.
- Investigate whether hypoglycemia or ketosis symptoms were present at the time of arrest.
- Challenge breath test results where medical conditions or interfering substances may have played a role.
- Consider whether an evidentiary breath test was the right choice at all for someone in ketosis, particularly when even the state’s own lab recognizes that fasting and dieting can have the same effect.
Internationally renowned breath test scientist coincidentally published a tremendously interesting, in-depth article on this very issue in the Counterpoint Journal shortly after our presentation. So we must really be on to something!
We’ve fought many battles over breath test science. Sometimes that means bringing in an expert; sometimes the smarter move is to use the government’s own training materials, manuals, and the operator’s testimony. The key is knowing when a machine’s number may be driven by biology, not booze.
Final Thought
As more people turn to these medications, we expect to see more “mystery” breath test results and more cases where medical metabolism, not alcohol consumption, is to blame.
In the fight for accurate, fair DWI prosecutions, this is an issue we can’t ignore.
