Cough & Flu Syrups & Breath Alcohol Testing: 

The Overlooked Risk of Mouth Alcohol Contamination

Counterpoint Volume 9: Issue 3 - Article 1 (September 2025)

Jan Semenoff, BA, EMA
​Forensic Criminalist

Article information:

Article - 1060 words (approximately 5-6 minutes)
Since the release of the myCAMprogram, I've been compiling a list of Over-the-Counter (OTC) medications and oral care products that should be avoided. Fuel cell devices, like those found in Ignition Interlock Devices (IIDs) do not employ a means for detecting inflated breath alcohol readings due to the recent consumption of any product containing ethanol, or any substances that looks like ethanol to the fuel cell. This will be the first of a few articles on the subject, starting with a likely culprit: Cold and flu medicines. 
​  - Editor

The Hidden Risk

Alcohol-containing cough syrups are among the most common over-the-counter medications. What many people fail to recognize is that these products can dramatically distort CAM program breath alcohol test results if administered without a proper observation and deprivation period.
This article examines the scientific basis for how cough syrup interferes with fuel cell devices (ignition interlocks; handheld portable breath testers) and underscores the necessity of standardized deprivation and wait period protocols to prevent false-positive results.
In a follow-up article, we will look at non-alcohol beverages such as "near-beer", and "mocktails", etc. You will be surprised to see the readings they generate of fuel-cell devices. Stay tuned...

A Case Example: Cough Syrup and a “Fail” on the Intoximeter Alco-Sensor FST

In one case, an individual consumed cough syrup shortly before using their ignition interlock device. The device locked out their vehicle, and produced a “FAIL” reading. A second test, only seven minutes later, yielded the same result. A CAM violation was recorded.
The problem: Cough syrup is a thick liquid suspension designed to coat the mouth and throat for therapeutic effect. Ethanol content in these syrups ranges from 5% to 25%, equivalent to the concentrations found in beer, wine, and some spirits. When present in the oral cavity, this residual ethanol produces artificially inflated BrAC readings that can persist for 15–20 minutes or longer.
Alcohol Concentrations in Over-the-Counter
Cold and Flu Medicines

Many liquid over-the-counter (OTC) cold and flu medicines contain alcohol, used as a solvent to help dissolve active ingredients. Alcohol concentrations vary widely ranging from as little as 1.4 percent to as high as 25 percent or more. It is essential to check the label of each product. In recent years, alcohol-free formulations have become widely available for many major brands. More problematically, depending on your source, the medication could or could not contain alcohol.

Alcohol Content in Specific Brands:

NyQuil
  • NyQuil Cold and Flu Nighttime Relief Liquid: Contains approximately (~) 10% alcohol.
  • NyQuil Cough Liquid: Generally may contain ~ 10% alcohol in many U.S./Canadian versions; claims of higher concentrations (e.g. ~25%) not supported by recent label data.
  • Alcohol-free options: NyQuil LiquiCaps and Alcohol-Free NyQuil Cold & Flu Nighttime Relief Liquid.

Robitussin
  • Historical and specific versions: Past formulas showed variable alcohol content. A 2004 listing indicated concentrations ranging from 2.1% (Robitussin DM) to 20% (Romilar CF). Some older formulations reportedly showed higher alcohol content, but reliable data is limited; many current versions are alcohol-free.
  • Alcohol-free options: Many modern Robitussin products, including Robitussin DM Coughgels and selected syrups, are alcohol-free.

Tylenol (Liquid)
  • TYLENOL Cold + Flu + Cough Night Liquid: Contains alcohol as primary inactive ingredient with no concentration listed.

​Other Products
  • DayQuil: Formulated as non-drowsy and generally alcohol-free. Listed as ~10-25% on some health care sources.
  • Theraflu: Some versions contain alcohol, with earlier formulas showing ~10%.
  • Children’s medicines: Most pediatric cough and cold medicines are alcohol-free, including Children’s NyQuil and Dimetapp.
  • Dristan Ultra: ~25%
  • Vick's Formula 44 D: ~20%
  • Vick's Formula 44 Cough: ~10%

How to Check for Alcohol Content:
  • Read the label: Look under the “Inactive Ingredients” section where alcohol content is listed. The alcohol may be "hidden" from view, and referred to as "dehydrated alcohol" or "alcohol USP".
  • Seek alcohol-free versions: Many brands clearly label products as “alcohol-free.”
  • Consult a pharmacist: Pharmacists are a reliable resource for questions about alcohol content and potential drug interactions.

Scientific Testing on Cough Syrups

Controlled experiments confirm that cough syrups cause roadside devices to report readings in the 0.300– 0.400 g/100 mL range immediately after consumption - values many times higher than legal per se limits. These readings decline over time, but remain falsely elevated for at least 15 minutes, sometimes longer, depending on the viscosity of the syrup and individual physiology.

The Deprivation and Observation Period: Why It Matters

​Breath alcohol testing protocols universally require a deprivation, wait, or observation period of at least 15 minutes before obtaining a breath sample (Dubowski, 1985; Jones, 1987; Gullberg, 2003). During this time, the subject must not eat, drink, smoke, burp, regurgitate, or place any substance in their mouth.
​The purpose is clear: To eliminate residual alcohol contamination from the oral cavity and ensure that the breath sample reflects alveolar (deep lung) air rather than transient mouth alcohol. Without this safeguard, results are inherently unreliable.
​In the cough syrup case, the subject did not wait for the required period. The result: contaminated samples and unreliable BrAC readings. A locked out device. A probation violation.

Mouth Alcohol and the Limits of Screening Devices

​Fuel cell-based ASDs, such as police roadside testers and ignition interlock devices, are particularly vulnerable to mouth alcohol contamination. Unlike evidentiary instruments, they lack built-in safeguards such as slope detectors or residual alcohol detection systems.
​Even where slope detectors are present, their reliability is questionable. Research indicates failure rates of 37% (Harding et al., 1992) and up to 48% (Simpson et al., 2004) in detecting mouth alcohol interference. Gullberg (2000) also reported inadequacies in these systems. In other words, even “sophisticated” evidentiary devices cannot always distinguish between true BrAC and mouth alcohol contamination.

Implications for Breath Alcohol Testing

​When cough syrup or any other alcohol-containing product is recently consumed, roadside or ignition interlock breath tests conducted without a proper deprivation period cannot be considered forensically reliable. The readings reflect a mixture of actual blood alcohol and residual mouth alcohol, producing falsely elevated results.
​This is not a minor procedural issue. Rather, it is a fundamental flaw in test validity. Any positive or “FAIL” result obtained under these conditions is open to serious scientific challenge.
​Practical Tip:
Before you use cold or flu medicine, you should confirm whether it contains alcohol. Cross-check with packaging or manufacturer data, as some formulations contain concentrations high enough to cause measurable false positives in breath or transdermal testing. Check with your pharmacist or health care provider for an alternative alcohol-free medicine to use instead. 

Conclusion

​Cough syrup is not a trivial factor in breath testing. With ethanol concentrations equal to alcoholic beverages, and a design that deliberately coats the throat and oral cavity, these medications create significant risks of false-positive BrAC readings.
​Without a 15–20 minute deprivation and observation period, supported by rinsing the mouth with water, breath test results are contaminated and scientifically unreliable. Fuel cell devices like ignition interlocks or personal breath alcohol testers, which lack residual alcohol safeguards, are especially prone to error.
​For people living under alcohol monitoring, the takeaway is straightforward: Breath test results following recent cough syrup consumption, absent of strict adherence to deprivation or wait period protocols, cannot be trusted as accurate measures of a person’s true breath alcohol concentration.

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For further study:

  1. Dubowski, K.M., “Quality Assurance in Breath-Alcohol Analysis”, Journal of Analytical Toxicology, Vol. 18, Oct 1994.
  2. Dubowski, K.M., “Acceptable Practices for Evidential Breath-Alcohol Testing”, Center for Studies of Law in Action, Borkenstein Course Materials, Indiana University, May 2008.
  3. Gullberg, R.G., “The Inadequacy of Instrumental “Mouth Alcohol” Detection Systems in Forensic Breath Alcohol Measurement”, Northwest Association of Forensic Sciences, Oct. 2000.
  4. Gullberg, R. G., “Breath Alcohol Measurement Variability Associated with Different Instrumentation and Protocols, Forensic Science International 131 (2003) 30-35.
  5. Harding, P., and McMurray, M., et al, The Effect of Dentures and Denture Adhesives on Mouth Alcohol Retention, Journal of Forensic Sciences, July 1992, Vol. 37, No. 4, pp. 999-1007.
  6. Hlastala, M., Lam, W., and Nesci, J., “The Slope Detector Does Not Always Detect the Presence of Mouth Alcohol”, For the Defense, March 2006.
  7. Jones, A. W., “Concerning Accuracy and Precision of Breath-Alcohol Measurements”, Clinical Chemistry, 33/10, 1701-1706 (1987).
  8. Semenoff, J., “Breath testing Error Message, Part 4 – Invalid Samples”, Counterpoint, Volume 2, Issue 4; Article 2, Spring 2018.
  9. Semenoff, J., “The Importance of the Wait, Deprivation or Observation Period”, Counterpoint, Volume 3, Issue 1; Article 1, Fall 2018.
  10. Sterling, K., “The Rate of Dissipation of Mouth Alcohol in Alcohol Positive Subjects”, The Journal of Forensic Science, 2011.