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Defenses to Drunk Driving

If you've been charged with a DUI, DWI, or drunk driving, you have a few options for mounting a criminal defense. Some affirmative defenses apply in rare circumstances, even when evidence supports the charge.

It's more common to defend against a drunk driving charge by attacking the police officer's observations of what happened before the arrest or challenging the integrity of the evidence, such as the accuracy of a Breathalyzer test, presence of slurred speech, or odor of alcohol. State DUI laws differ, and everyone's case has different facts, so it may help to consult a lawyer.

This article discusses affirmative defenses to DUI charges. It also addresses common drunk driving legal defenses. Finally, less common defenses are covered.

Affirmative Defenses to DUI Charges

An affirmative defense is a fact or set of facts that, if proven, negates liability for otherwise unlawful conduct. An affirmative defense is a justification or excuse for specific behavior. Below are numerous affirmative defenses to a driving under the influence (DUI) charge.


Necessity as an affirmative defense arises when a person must drive to prevent a greater evil. The driver must prove they had no other options and that the greater evil they wished to avoid was more serious than the potential harm caused by a DUI.


This affirmative defense can be applied when a motorist drives to avoid serious injury or death. An example of driving under duress would be someone forcing an intoxicated person to drive by threat of force.


When a law enforcement officer somehow encourages a motorist to become intoxicated or drive while under an impairment, that gives rise to entrapment. The motorist must also prove they wouldn't have been predisposed to drive drunk but for the alleged entrapment.

Mistake of Fact

A mistake of fact arises when a driver honestly believes they're not intoxicated. For example, a mistake of fact can arise if you have a valid reason to think the impairing effect of your prescription medication has worn off before you drive a motor vehicle.

Involuntary Intoxication

Involuntary intoxication occurs when you ingest alcohol without your knowledge. For example, suppose the punchbowl at a party was "spiked" with an otherwise unrecognizable quantity of liquor. In that case, involuntary intoxication might be a viable affirmative defense to driving under the influence of alcohol.

Common Drunk Driving Defenses

Below are some common bases for defending against a drunk driving charge.

Improper Stop

This is one of the most common defense strategies defense attorneys use in DUI cases. This argument claims the arresting officer lacked reasonable suspicion or probable cause to make the initial traffic stop. For instance, your attorney might claim you didn't commit a traffic violation.

Administration/Accuracy of Field Sobriety Test

A DUI arrest may be ruled improper if it was based on an improperly administered field sobriety test or inaccurate test results. The horizontal gaze nystagmus (HGN) test, which detects eye movements often associated with intoxication, is frequently challenged.

Administration/Accuracy of Portable Breathalyzer Test

Your attorney may challenge the administration of the Breathalyzer or other chemical test used at the scene of your arrest. Your attorney can claim the officer wasn't properly trained to conduct the breath alcohol testing.

Your lawyer may also claim intervening factors, such as vomiting or indigestion, affected breath test results. Additionally, the defense may question whether the breath test device was properly calibrated and maintained.

Administration/Accuracy of Standard Breathalyzer Test

This defense is similar to the one raised above. However, it pertains to the more accurate breath test devices used at the police station after an arrest.

Administration/Chain of Custody of Blood Test

This defense raises questions about the administration of a blood test and whether it was tampered with or otherwise mishandled in the chain of custody.

Rising Blood Alcohol Concentration

Your criminal defense lawyer can claim your blood alcohol concentration (BAC) was below the legal limit while you were driving but increased between the time of your traffic stop and the administration of your breath test. This is possible when recently consumed alcohol has yet to fully absorb into your system until the time of the BAC test.

Other, Less Common Defenses

Below are two other defenses to a DUI charge. However, they're less commonly employed.

The Accused Person Wasn't the Driver

Questions may arise over whether the person charged with the DUI was driving at the time. Perhaps the passenger, believing they were sober, switched places with the driver but failed a sobriety or breath test.

Improper Police Actions

This defense may include evidence or testimony that the officer violated the accused's civil rights, faked a DUI report, or otherwise acted improperly.

A DUI Defense Attorney Can Help Argue Your Defenses to a Drunk Driving Charge

Even if you think you may have been at least a little inebriated when you were pulled over and arrested for driving under the influence, you still have the right to a misdemeanor DUI defense. To increase your chances of avoiding a DUI conviction, it's in your best interest to contact a DUI lawyer. Find a local DUI attorney today to help you with things like license suspension following a DUI.

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  • Complex DUI situations usually require a lawyer
  • DUI defense attorneys can challenge Breathalyzer/Intoxilyzer or blood test results
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