Rising Blood Alcohol as a Defense to DUI Charges

“Rising blood alcohol” is a common legal defense to driving under the influence. It is based on the fact that blood alcohol concentration (“BAC”) levels continue to rise even after you stop drinking.¹

When you consume alcohol, your blood alcohol rises rapidly. It continues to rise until it peaks anywhere from 30 minutes to two hours later.

So even though your BAC may be over the “legal limit” by the time a breath test or blood test is administered, it may have been below the legal limit when you were actually driving.

In most states, driving with a BAC of .08% is an automatic DUI. The rising blood alcohol defense works best when your test results are near the legal limit, as following timeline illustrates.

In this article, our California DUI lawyers discuss 7 key things to know about the rising blood alcohol defense:

• 1. What is “rising blood alcohol”?
• 2. How is alcohol absorbed in the human body?
• 3. How do BAC levels change over time?
• 4. Factors that affect the rate at which BAC rises
• 5. How can”rising blood alcohol” lead to a false result on a DUI chemical test?
• 6. How can I use “rising blood alcohol” to fight DUI charges?
• 7. Is an expert witness required?
• Additional Reading

1. What is “rising blood alcohol”?

“Rising blood alcohol” is a defense used in some drunk driving charges. It results from the fact that it takes time for the body to fully metabolize alcohol.

After alcohol consumption, BAC rises rapidly and steadily. It continues to do so until it reaches its maximum level or “peak.” This peak occurs, on average, 30 to 45 minutes after alcohol is consumed.²

Depending on your chemistry and circumstances, it can take longer. Sometimes it can take two or even three hours for blood alcohol to reach its peak. ³

This means that if you are below the legal limit when you are pulled over, you may still have a BAC that is “on the rise.” By the time a DUI chemical test is performed, your BAC may have crept over the legal limit.

For more discussion, see our page on How long does alcohol stay on your breath?

2. How is alcohol absorbed in the human body?

When you consume alcohol, 20% is absorbed in the stomach. Most of the remaining 80% is absorbed in the small intestine.⁴ A small amount is excreted in:

• sweat,
• saliva,
• urine, and
• breath.

This is how DUI breath tests can detect it.⁵ From the digestive system, the alcohol passes into the bloodstream. The blood then carries it to the brain and other organs.⁶

Eventually, the alcohol is metabolized (broken down) by the liver. It is then eliminated, primarily in the urine.⁷

However, the liver can only metabolize so much alcohol at one time. Whatever it cannot metabolize remains in the blood until the liver catches up.⁸ This is what results in you becoming intoxicated.

3. How do BAC levels change over time?

After rapidly reaching a peak 30 minutes to two hours after alcohol is consumed, BAC begins to decline at a more gradual rate. This decline is sometimes referred to as “falling blood alcohol.”

This change in BAC over time–rising blood alcohol followed by falling blood alcohol–can be represented graphically, as in the “blood alcohol curve” shown below.

100 mg% represents a BAC of .08%. Note that BAC would be lower if the same number of drinks had been consumed over a longer period of time. (Graph courtesy of the National Institute on Alcohol Abuse and Alcoholism.)

4. Factors that Affect the Rate at Which BAC Rises

Numerous factors can affect the rate at which alcohol is absorbed and eliminated. Such factors include:

• The type of drink consumed (for example, beer versus hard liquor),⁹
• Whether the alcohol was consumed on a full or empty stomach,
• How quickly the drink was consumed,
• Your height, weight, or body type/body fat percentage,
• Your gender,
• Your functional tolerance for alcohol,
• Drug interactions,
• Illness, and
• Fatigue.¹⁰

5. How can”rising blood alcohol” lead to a false result on a DUI chemical test?

Chemical tests are not given immediately after you are pulled over. Often, they are not performed until after you have been arrested and taken to the police station.

DUI chemical test results are generally considered valid if given within three hours after an arrest.¹¹ So some people’s BAC will still be “on the rise” or peaking at the time of the test.

Others will have falling blood alcohol. Though, as we have seen, BAC falls more slowly than it rises. So even though it is falling, it may not have fallen all the way back to where it was at the time of driving.

Example: When Caroline gets into her car, her BAC is at around .06%–below the legal limit of .08% in most states. Her driving ability is not impaired. So she is not driving “under the influence” of alcohol.¹² However, Caroline swerves into the next lane over while checking her smartphone. An officer pulls her over and smells alcohol on her breath.

When Caroline refuses to take a preliminary alcohol screening (“PAS”) breath test, the officer arrests her for DUI. Carolina’s BAC continues to rise while she is transported to the police station. As a result, by the time she takes a breath test at the station, she “blows” a .09%. She is charged with violating Vehicle Code 23152(b), California’s DUI “per se” law. ¹³

6. How can I use “rising blood alcohol” to fight DUI charges?

An experienced DUI defense lawyer and expert witness can “back out” your likely BAC at the time of driving. This defense is especially useful when your BAC is at – or close to – the legal limit.

Often this is enough to create reasonable doubt about whether you were over the limit. Or it might convince the prosecutor to dismiss the charges or agree to a plea deal, such as to:

• A “wet reckless” plea bargain,
• A “dry reckless” charge reduction, or
• A plea to an “exhibition of speed.”

7. Is an expert witness required?

Establishing a rising blood alcohol defense almost always requires testimony from a DUI defense expert witness.

By law, a DUI chemical test is considered accurate until proven otherwise.¹⁴ This shifts the burden on you to prove that the chemical test results were not accurate.

Doing this usually requires a forensic toxicologist. This expert will consider all of the relevant factors and construct a personal BAC timeline.

Example: A police officer stopped Bonnie at 7:20 PM. Bonnie agreed to a PAS breath test 10 minutes later, which showed that Bonnie’s BAC was at .08%.  After her arrest for DUI, Bonnie elected a post-arrest breath test. It showed a BAC of .09%.

This is strong evidence that Bonnie’s blood test was still rising when she drove. Her BAC was likely below .08% when she was pulled over. Unless there is evidence that Bonnie’s driving was actually impaired, she should not be convicted of DUI.¹⁵

Often, a DUI defense expert’s conclusions can be presented to the prosecution before trial. Sometimes this will get the charges thrown out. Or, at the very least, an experienced DUI defense lawyer can negotiate a plea bargain to a lesser charge.

Even if the case goes to trial, the expert’s testimony about rising BAC might:

• Discredit the prosecution’s expert witness, and
• Establish reasonable doubt that you were over the legal limit (or even impaired) when you drove.

Additional Reading

For more in-depth information, refer to these scholarly articles:

• Effect of Time Interval between the Traffic Case and Alcohol Test on the Legal Blood Alcohol Limit in Traffic Accidents – Journal of Faculty of Pharmacy of Ankara University.
• States of Consciousness and Alcohol: Relationship to the Blood Alcohol Curve, Time of Day, and the Menstrual Cycle – Alcohol Health and Research World.
• Retrograde Extrapolation of Blood Alcohol Concentration – Criminal Law Bulletin.
• Ascending and descending rates of change in blood alcohol concentrations and subjective intoxication ratings – Journal of Substance Abuse.
• The Course of the Blood-Alcohol Curve After Consumption of Large Amounts of Alcohol under Realistic Conditions – Canadian Society of Forensic Science Journal.

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Legal References:

1. See, for example, National Highway Traffic Safety Administration, “Alcohol Effects on People.”
2. National Institute on Alcohol Abuse and Alcoholism, Alcohol Alert No. 35.
3. Medicine.net, “Alcohol and Nutrition,” Third Section (“How is alcohol metabolized?”).
4. Same.
5. Same.
6. Same.
7. Same.
8. Same.
9. Same.
10. See, for example, Stanford University, Office of Alcohol Policy and Education, “Factors That Affect How Alcohol is Absorbed & Metabolized.”See also Mack C. Mitchell, Jr., Erin L. Teigen, and Vijay A. Ramchandani, “Absorption and Peak Blood Alcohol Concentration After Drinking Beer, Wine, or Spirits,” Alcohol Clin Exp Res. 2014 May; 38(5): 1200–1204. (“Findings indicate that BAC is higher after drinking vodka/tonic than beer or wine after fasting.”).
11. See, for example, Vehicle Code 23152(b) VC, California’s “DUI” per se law: “It is unlawful for a person who has 0.08 percent or more, by weight, of alcohol in his or her blood to drive a vehicle. For purposes of this article and Section 34501.16, percent, by weight, of alcohol in a person’s blood is based upon grams of alcohol per 100 milliliters of blood or grams of alcohol per 210 liters of breath. In any prosecution under this subdivision, it is a rebuttable presumption that the person had 0.08 percent or more, by weight, of alcohol in his or her blood at the time of driving the vehicle if the person had 0.08 percent or more, by weight, of alcohol in his or her blood at the time of the performance of a chemical test within three hours after the driving.”
12. See, for example, California Vehicle Code 23152(a): “It is unlawful for a person who is under the influence of any alcoholic beverage to drive a vehicle.”See also California Criminal Jury Instructions (CALCRIM) 2110. Driving Under the Influence: “A person is under the influence if, as a result of (drinking [or consuming] an alcoholic beverage/ [and/or] taking a drug), his or her mental or physical abilities are so impaired that he or she is no longer able to drive a vehicle with the caution of a sober person, using ordinary care, under similar circumstances.”
13. Same.
14. See, for example, California Vehicle Code 23152(b).
15. See California Vehicle Code 23152(a). This section makes impaired driving a crime, even when the driver’s BAC is under the “legal limit.”