In Missouri v. McNeely, 569 U.S. 141 (2013), the Supreme Court held that the natural breakdown of alcohol in a person’s bloodstream does not, by itself, create the kind of emergency that lets police draw blood from a DUI suspect without a warrant. Officers have to look at the actual facts of the stop and decide whether getting a warrant was realistically possible. If it was, and they didn’t try, the blood evidence can be thrown out.1Justia. Missouri v. McNeely, 569 U.S. 141
The decision rejected what had become a common practice in many police departments: treating every drunk-driving arrest as an automatic emergency because alcohol levels drop over time. That shortcut is no longer good enough on its own.
What the Court Held
Justice Sotomayor wrote the opinion, joined on the core holding by Justices Scalia, Kennedy, Ginsburg, and Kagan. A blood draw is a search under the Fourth Amendment. It pierces the skin and takes part of a person’s body, which the Court described as a significant physical intrusion demanding strong constitutional protection. A warrantless search of a person is reasonable only if it fits a recognized exception, and the state has to prove the exception applies.1Justia. Missouri v. McNeely, 569 U.S. 141
Missouri argued that because blood alcohol concentration falls over time, every DUI investigation is automatically an emergency that lets officers skip the warrant. The Court disagreed. Alcohol dissipation can support an emergency finding when combined with other facts, as it did in the older case of Schmerber v. California, where an officer was tied up with an accident scene and injured occupants. But it does not create a blanket rule that applies to routine stops.2Justia. Schmerber v. California, 384 U.S. 757
The majority also pointed out that the world has changed since 1966. In many jurisdictions officers can now request warrants by phone or email, sometimes receiving approval in under 30 minutes. Federal Rule of Criminal Procedure 41 already allows warrant applications by telephone or other reliable electronic means, and many state systems mirror that.3Legal Information Institute. Federal Rules of Criminal Procedure Rule 41 – Search and Seizure The “no time for a warrant” argument gets weaker every year as those systems spread.
The Facts Behind the Case
At about 2:08 a.m. in Cape Girardeau County, Missouri, a highway patrol officer stopped Tyler McNeely for speeding and crossing the centerline. McNeely had bloodshot eyes, slurred speech, smelled of alcohol, and admitted to a couple of beers. He failed field sobriety tests and refused a portable breath test. The officer arrested him.1Justia. Missouri v. McNeely, 569 U.S. 141
When McNeely said he’d refuse a station breath test too, the officer drove him to a hospital instead. He never tried to get a warrant. McNeely refused to consent to a blood draw, and the officer directed a lab technician to take it anyway. Blood was drawn at roughly 2:35 a.m., about 27 minutes after the stop. It came back at 0.154 percent, nearly double the legal limit.1Justia. Missouri v. McNeely, 569 U.S. 141
Because McNeely had two prior DUI convictions, this was a class D felony with up to four years in prison. The trial court suppressed the blood test, finding no emergency that justified skipping the warrant. Missouri fought the suppression all the way to the Supreme Court and lost.
The Totality of the Circumstances Test
Instead of drawing a bright line, the Court told judges to look at everything about a specific stop when deciding whether a warrantless blood draw was justified. No two DUI arrests get treated identically. The officer’s timeline and choices are examined in detail after the fact.
The factors that carry weight include how much time the officer actually had before evidence would meaningfully degrade, whether a magistrate was reachable by phone or electronic system in that jurisdiction, whether the officer was simultaneously handling injured victims or a complex scene, and how remote the location was. A quiet traffic stop with one cooperative suspect and an on-call judge available by phone is very different from a multi-car crash with injuries and a single officer on scene.
The point of the test is to stop the government from using a one-size-fits-all excuse to bypass judicial oversight. If a reasonable officer in the same position could have obtained a warrant without losing useful evidence, a warrantless draw likely violates the Fourth Amendment.
When Warrantless Blood Draws Still Work
McNeely did not ban warrantless blood draws. It narrowed the exception to genuine emergencies where something beyond ordinary alcohol dissipation made a warrant impractical.
A serious multi-vehicle accident is the clearest example. When an officer has to secure a scene, coordinate ambulances, direct traffic, and manage multiple suspects, the practical demands can consume the available time. If the officer can document those pressures, the blood evidence may survive a suppression challenge. The prosecution has to show those specific hurdles existed.
Medical emergencies involving the suspect can also create real exigency. If someone needs surgery and IV fluids would dilute the blood alcohol evidence, waiting for a warrant might destroy the evidence entirely. What will not survive is an officer simply choosing not to bother, or a department policy of never seeking warrants for DUI blood draws.
What Happens When a Blood Draw Violates the Fourth Amendment
If a court decides a warrantless blood draw was unconstitutional, the blood alcohol result is typically suppressed under the exclusionary rule. Prosecutors cannot use the BAC number at trial. That often gutts the case, especially at felony levels, because what’s left is the officer’s observations and field sobriety test performance, which are harder to build a conviction on.
That is exactly what happened to the trial court’s ruling in McNeely’s own case. The 0.154 reading came out. For defense attorneys, the framework creates a viable path to challenge blood evidence in nearly any DUI case where the officer did not seek a warrant. The prosecution has to affirmatively prove exigent circumstances, not just assert that alcohol was dissipating.
Breath Tests Are Treated Differently: Birchfield v. North Dakota
Three years after McNeely, the Court drew a sharp line between breath and blood in Birchfield v. North Dakota, 579 U.S. ___ (2016). Warrantless breath tests are permitted as a routine part of a lawful DUI arrest. Warrantless blood tests are not.4Justia. Birchfield v. North Dakota, 579 U.S. ___ (2016)
The difference is how invasive each test is. A breath test captures air you’re already exhaling and reveals only alcohol concentration. A blood draw pierces the skin and extracts a sample that can reveal far more. Because breath tests are much less intrusive and serve law enforcement interests in most cases, they qualify as a search incident to arrest without a warrant.
Birchfield also addressed criminal penalties for refusing testing. States can civilly and administratively penalize refusal of either test. They can criminally punish refusal of a breath test, because that search needs no warrant. They cannot criminally punish refusal of a blood test.4Justia. Birchfield v. North Dakota, 579 U.S. ___ (2016)
Unconscious Drivers: Mitchell v. Wisconsin
In Mitchell v. Wisconsin, 588 U.S. ___ (2019), a plurality of the Court concluded that when a suspected drunk driver is unconscious and cannot take a breath test, the exigent circumstances doctrine will almost always permit a warrantless blood draw.5Justia. Mitchell v. Wisconsin, 588 U.S. ___ (2019)
The reasoning is that unconscious drivers present compounding emergencies. The person typically needs immediate medical attention. Transport and treatment can alter blood composition. Officers on scene are handling medical priorities, not sitting idle with time to draft a warrant application. That combination fits the kind of multi-factor emergency McNeely contemplated.
The plurality left a narrow opening for defendants to show blood would not have been drawn anyway for medical reasons and that a warrant application would not have interfered with other pressing needs. In practice, this exception will rarely apply when someone is found unconscious behind the wheel.
Implied Consent and Refusing a Test
Every state has some form of implied consent law. By driving on public roads, you have already agreed in advance to submit to a chemical test if an officer has probable cause to suspect impaired driving. Those laws existed long before McNeely and still apply. What changed is what consequences states can attach to refusal.
Refusing a chemical test after a DUI arrest typically triggers administrative penalties separate from any criminal case, most commonly an automatic license suspension ranging from about 180 days to one year for a first refusal. Many states allow prosecutors to introduce the refusal itself as evidence of guilt. Some jurisdictions require an ignition interlock device once driving privileges are restored.
After Birchfield, the constitutional line is clear: states can criminally punish refusal of a breath test, but not refusal of a blood test. Civil and administrative penalties for refusing either remain valid. In practice, officers will typically offer a breath test first. Blood draws come up when a breath test is unavailable, when the suspect is unconscious, or when officers have specific reasons to want blood. In those situations the officer generally needs a warrant unless a real emergency exists under the McNeely framework.
If your blood was drawn without a warrant, the questions your lawyer will ask track the McNeely analysis directly. How long did the stop take? Was an on-call magistrate or electronic warrant system available in that county? Was the officer managing anything besides your arrest? The answers often decide whether the BAC number makes it into evidence at all.