A motorist charged with a DUI or DWI (the actual charge commonly referred to as "drunk driving") has a few different options when it comes to mounting a defense. Some affirmative defenses exist in very rare circumstances, even when the evidence otherwise supports the charge. But it's more common to defend against a drunk driving charge by attacking the officer's observations of what happened prior to the arrest or challenging the integrity of the evidence, such as the accuracy of a breathalyzer test. State DUI laws differ and everyone's case has different facts, so it may help to consult with a lawyer.

Affirmative Defenses to DUI Charges

1. Necessity - When a person must drive to prevent a greater evil. The driver must prove that he or she had no other options and that the "greater evil" they wished to avoid was more serious than the potential harm caused by a DUI.

2. Duress - When the defendant drives in order to avoid serious injury or death, he or she is doing so under duress. For example, someone forces an intoxicated person to drive by threat of force.

3. Entrapment - When an officer somehow encourages a motorist to become intoxicated or drive while under the influence, it is referred to as entrapment. The defendant must also be able to prove that he or she would not have been predisposed to drive drunk if not for the alleged entrapment.

4. Mistake of Fact - When a person has an honest belief that he or she is not intoxicated. For example, having a valid reason to believe that the impairing effect of one's prescription medication has worn off.

5. Involuntary Intoxication - When a person has ingested alcohol without his or her knowledge. For example, if the punchbowl at a party was "spiked" with an otherwise unrecognizable quantity of liquor.

Common Drunk Driving Defenses

1. Improper Stop - This is one of the most common arguments used by defense attorneys in DUI cases, and involves the claim that the officer lacked probable cause to make the initial traffic stop.

2. Administration / Accuracy of Field Sobriety Test - An arrest may be ruled improper if it was based on an improperly administered field sobriety test or inaccurate results. The horizontal gaze nystagmus (HGN) test, which detects eye movements often associated with intoxication, is frequently challenged.

3. Administration / Accuracy of Portable Breathalyzer Test - The attorney may challenge the administration of the breathalyzer test used at the scene (i.e. was the officer properly trained?) or whether there were intervening factors such as vomiting or indigestion. Also, the defense may question whether the breath test device was properly calibrated and maintained.

4. Administration / Accuracy of Standard Breathalyzer Test - Similar defense to #3, but pertaining to the more accurate breath test devices used at the police station after an arrest is made.

5. Administration / Chain of Custody of Blood Test - This defense raises questions about the administration of a blood test and/or whether it was tampered with or otherwise mishandled in the chain of custody.

6. Rising Blood Alcohol Concentration - Defense claims the BAC was below the legal limit while the defendant was driving but actually increased between the time of the traffic stop and the administration of the breath test. This is possible when recently consumed alcohol has yet to fully absorb into the system until the time of the BAC test.

Other, Less Common Defenses

1. Accused was not the Driver - Questions may arise over whether the person charged with the DUI actually was driving at the time. Perhaps the passenger, believing he or she was sober, switched places with the driver but failed a sobriety or breath test.

2. Improper Police Actions - This defense may include evidence and/or testimony that the officer violated the defendant's civil rights, faked a DUI report or otherwise acted improperly.

An 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 defense. In order to protect your rights and get the best outcome possible, it's in your best interests to contact a legal professional. Find a local DUI attorney today.