What is the implied consent law?

Why the law works this way

A driver's license is treated as a privilege granted by the state, and one condition of that privilege is agreeing in advance to be tested when there is lawful reason to suspect impaired driving. The idea is to get reliable evidence quickly, before alcohol leaves the body. You can still refuse in the moment — officers will not physically force a breath test — but the refusal itself carries consequences.

When it applies

Implied consent usually applies only after a lawful arrest for DUI, or when the officer has probable cause to believe you were driving impaired. The officer must normally warn you about the consequences of refusing, often by reading a standard advisory. If the stop or arrest itself was unlawful, the test result — or the refusal — can sometimes be excluded.

What refusal normally costs

• An automatic license suspension, commonly 6 to 18 months for a first refusal and longer for repeats — often longer than the suspension for failing the test.
• Admissibility of the refusal as evidence at trial in most states, where prosecutors argue it shows consciousness of guilt.
• In some states, a separate offense or an enhanced sentence on conviction, and mandatory ignition interlock on reinstatement.
• Loss of a hardship or work license in states that deny restricted driving privileges after a refusal.

Roadside tests are a different thing

Implied consent covers the evidentiary test after arrest, usually on a certified breath machine at the station or a blood draw at a hospital. Preliminary roadside breath tests and field sobriety exercises — walk-and-turn, one-leg stand, following a pen with your eyes — are, in most states, voluntary for adult drivers, though refusing them can contribute to probable cause. Commercial drivers and drivers under 21 face stricter rules almost everywhere, including penalties for refusing a roadside test in some states.

Watch

The blood-test limit

In Birchfield v. North Dakota (2016) the Supreme Court held that a breath test may be required incident to a lawful DUI arrest, but a blood draw generally requires a warrant or valid consent, and a state may not make refusal of a warrantless blood test a crime. Missouri v. McNeely (2013) had already held that the natural dissipation of alcohol does not by itself justify a warrantless blood draw. Mitchell v. Wisconsin (2019) added that an unconscious driver will usually fall within the exigent-circumstances exception. In practice, many police departments now obtain electronic warrants for blood within an hour.

Drugs and urine tests

Implied consent laws also cover testing for drugs, including marijuana and prescription medications. Because there is no widely accepted roadside device for measuring drug impairment, officers often rely on a drug recognition expert evaluation and a blood test. Some states set per se limits for THC; others require proof of actual impairment.

Should you refuse?

There is no universal answer, and a lawyer cannot give it to you at the roadside. Refusal can deprive the prosecution of a number, but it brings its own suspension, is usually admissible, and in many states is punished more harshly for repeat offenders. People with prior DUIs face the steepest refusal penalties. The decision is most often discussed after the fact, in deciding how to fight the case.

The deadline nobody tells you about

The license suspension is an administrative action by the motor vehicle department that runs on its own track, separate from the criminal case. Most states give only 7 to 30 days from the arrest to request a hearing, and missing that window forfeits the license challenge even if the criminal case is later dismissed. At the hearing, the issues are usually narrow: whether the officer had reasonable grounds, whether you were lawfully arrested, whether you were properly warned, and whether you actually refused.

What to do after an arrest

Write down everything you remember about the stop, the tests and what the officer said. Find the date on your temporary license or suspension notice, and contact a DUI lawyer quickly so the hearing request is filed on time. The hearing is also a chance to question the officer under oath before the criminal trial.