No, a breathalyzer cannot detect drugs. These devices are calibrated to measure one thing only: ethanol, the alcohol in beer, wine, and liquor. If an officer suspects you’re impaired by marijuana, opioids, cocaine, methamphetamine, or any other drug, the breathalyzer is useless for proving it, and a different set of tools comes into play.
Why Breathalyzers Only Register Alcohol
When you drink, ethanol enters your bloodstream and travels to your lungs. As blood moves through the small air sacs there, some of the ethanol evaporates into the air you exhale. A breathalyzer captures that exhaled air and measures its ethanol concentration, then converts the reading into an estimated blood alcohol content. The sensors inside, whether fuel cell or infrared, are built to react specifically to ethanol molecules.
Drug molecules are structured differently. THC from marijuana, morphine from opioids, and benzoylecgonine from cocaine do not behave in the lungs the way ethanol does, and most drugs are not expelled through breath in predictable, measurable concentrations. Even if trace amounts reached your exhaled air, the sensors would not recognize them. The device is not built for that job.
What Happens When the Breathalyzer Reads 0.00
A zero reading does not end a traffic stop if the officer still sees signs of impairment. This is the exact scenario that led the LAPD to create the Drug Recognition Expert program in the 1970s: officers kept arresting drivers who were clearly impaired but blew low or zero on alcohol tests.1International Association of Chiefs of Police. Drug Recognition Experts
Today, an officer who still suspects impairment after a 0.00 result will keep investigating. That typically means field sobriety tests, close observation of your eyes, speech, and coordination, and in many cases a call for a Drug Recognition Expert. If enough evidence of impairment accumulates, the officer can establish probable cause for a chemical test of your blood, urine, or oral fluid.
How Police Actually Detect Drug Impairment
Standardized Field Sobriety Tests
Three field tests are validated by NHTSA: the Horizontal Gaze Nystagmus test, where the officer watches your eyes track a moving stimulus; the Walk-and-Turn test; and the One-Leg Stand test.2National Highway Traffic Safety Administration. DWI Detection and Standardized Field Sobriety Testing Participant Manual These assess coordination, balance, and the ability to follow instructions while dividing your attention. They can indicate impairment, but they cannot tell the officer what substance is causing it.
Drug Recognition Experts
A Drug Recognition Expert is a police officer certified through a program jointly run by the International Association of Chiefs of Police and NHTSA.3International Association of Chiefs of Police. What They Do A DRE conducts a systematic 12-step evaluation that goes well beyond standard field sobriety tests.
The evaluation includes a breath alcohol test to rule out or quantify alcohol, an interview with the arresting officer, a preliminary physical exam with pulse checks, detailed eye examinations, four divided-attention tests (Modified Romberg Balance, Walk and Turn, One Leg Stand, and Finger to Nose), vital signs, dark room pupil examinations, muscle tone checks, a search for injection sites, and a subject interview. The DRE then forms an opinion about whether the person is impaired and, if so, which drug category is likely responsible. A toxicological exam follows to confirm or refute that opinion.4National Highway Traffic Safety Administration. DRE Preliminary School Participant Manual
Blood, Urine, and Oral Fluid Tests
Chemical testing is the only way to confirm which drugs are actually in someone’s system. Blood tests are the most reliable for measuring drug concentrations and are widely accepted in court. Urine tests detect metabolites but say little about impairment at the time of driving, because metabolites can linger for days or weeks after a drug’s effects have worn off. Oral fluid testing detects parent drugs rather than metabolites, so it reflects recent use somewhat better.5American Bar Association. Testing Challenges: No BAC for THC
Roadside Oral Fluid Screening
Roughly half the states now have statutes authorizing roadside oral fluid tests, where an officer swabs the inside of your cheek and runs a rapid screening panel. These tests can flag several drug categories within minutes. The limitations are real, though. Manufacturers label the results as presumptive, meaning they require laboratory confirmation. Cross-reactivity with legal substances can produce false positives. There are no consistent manufacturing standards across brands, and analog kits require the officer to visually interpret the result, which introduces subjectivity. State laws on how the results can be used vary widely.
Is a Drug Breathalyzer Coming?
Researchers are working on it, but the technology is not ready. Several cannabis breath tests are being piloted by law enforcement agencies around the country, and there is still no scientific consensus on whether they work reliably.6National Institute of Standards and Technology. NIST Researchers Test New Approach for Detecting Cannabis in Breath
The core problem is telling recent use apart from past use. NIST and University of Colorado researchers found that regular cannabis users can have THC levels in their breath on days they haven’t smoked that are similar to levels measured an hour after use.6National Institute of Standards and Technology. NIST Researchers Test New Approach for Detecting Cannabis in Breath Connecting a breath reading to actual impairment behind the wheel is close to impossible on that basis.
Laboratory studies have shown exhaled breath can carry detectable traces of many substances. One analysis identified 22 substances tied to 19 different illicit drugs, including metabolites of cocaine, heroin, methadone, and methylphenidate, with detection windows estimated at 24 to 48 hours after use.7Nature. Screening of Drugs in Exhaled Breath by UHPLC-MS/MS in a Nightlife Setting Lab feasibility is not roadside reliability. No breath-based drug test has been validated to the legal standards alcohol breathalyzers meet, and none are admissible as evidence of impairment in court today.
Can You Refuse a Drug Test?
Every state has an implied consent law. By driving on public roads, you have already agreed in advance to submit to chemical testing if an officer has probable cause to believe you’re impaired. These laws started with alcohol but now cover drugs in most states, with some authorizing blood, oral fluid, and urine testing for drug impairment and a handful limiting drug testing to crashes involving death or serious injury.
Refusing carries its own penalties, separate from any DUID charge. The most common consequence is an administrative license suspension, which happens automatically through the motor vehicle agency rather than through a criminal conviction. In many states, the suspension for refusal is longer than the suspension for a first-offense DUID, precisely because the law is designed to discourage refusal.
There is a constitutional wrinkle. In Birchfield v. North Dakota, the U.S. Supreme Court held that while police can require a breath test incident to a drunk driving arrest without a warrant, they cannot require a warrantless blood test. Because breath tests do not detect drugs, officers investigating drug impairment generally need your consent, a warrant, or qualifying exigent circumstances to draw blood. The Court specifically noted that when substances other than alcohol impair driving, “nothing prevents the police from seeking a warrant.”8Justia. Birchfield v North Dakota
Prescription Medications Are Not a Safe Harbor
Having a valid prescription is not a defense against drug-impaired driving charges in most states. If a legally prescribed medication substantially impairs your ability to drive safely, you can be arrested and convicted just as you would be for an illegal drug. This covers opioid painkillers, benzodiazepines like Xanax or Valium, sleep medications, muscle relaxants, and certain antihistamines.
Some states allow a limited defense if you held a valid prescription and took the medication exactly as directed. Even that defense fails when the circumstances suggest you should have known driving was unsafe. Taking a prescribed sleep aid and then deciding to run an errand would almost certainly defeat the argument. The warning labels on these medications are essentially the legal standard prosecutors will hold you to.
The Bottom Line for Drivers
If you are stopped and the officer suspects drugs, blowing 0.00 on a breathalyzer will not end the investigation. The device confirms you are not over the alcohol limit; it says nothing about drugs in your system. From there, the officer’s attention shifts to field sobriety performance, physical signs, possibly a DRE evaluation, and ultimately a blood, urine, or oral fluid test that can identify specific substances.