Rising Blood Alcohol as a Defense to DUI Charges

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

When someone consumes an alcoholic beverage, blood alcohol rises rapidly. It continues to rise until it reaches a peak level anywhere from 30 minutes to two hours later. Thus even though a motorist's BAC may be over the “legal limit” by the time a DUI breath test or DUI blood test is administered, it may have been below the legal limit when he or she was actually driving.

In this article, our California DUI defense lawyers discuss7 key things to know about the "rising blood alcohol" defense"

breathalyzer rising blood alcohol california legal defense
“Rising blood alcohol” is a legal defense used in some drunk driving charges.

1. What is "rising blood alcohol"?

“Rising blood alcohol” is a legal 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, 30-45 minutes after alcohol is consumed.2

But depending on individual 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 a driver who is below the legal limit when he/she is pulled over may still have a BAC that is “on the rise.” By the time a DUI chemical test is performed, the driver's BAC may have crept over the legal limit.

2. How is alcohol absorbed in the human body?

When someone consumes an alcoholic drink, approximately 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 how DUI breath tests and rune 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

But the liver can only metabolize so much alcohol at one time. Whatever it can't metabolize remains in the blood until the liver catches up.8 This is what results in someone becoming intoxicated.

3. How do BAC levels change over time?

After rapidly reaching a peak 30 minutes to 2 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.

Blood alcohol content over time legal defense california
Average blood alcohol concentration (BAC) after the rapid consumption by eight male subjects on an empty stomach.

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 (e.g., beer versus hard liquor),9
  • Whether the alcohol was consumed on a full or empty stomach,
  • How quickly the drink was consumed,
  • Body type/body fat percentage of the person drinking,
  • The drinker's gender,
  • The drinker's 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 always given immediately after a suspect is pulled over. Often, they are not performed until after a driver has been arrested and taken to the police station.

DUI chemical test results are generally considered valid if given within three (3) 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. But, 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: Caroline arrives at a party in Los Angeles at 6 PM. She has a drink and some snacks right away. After a couple of hours, she has another drink. Her liver can easily metabolize the drinks at this pace.

An hour later Caroline decides it's time to go. She has one last drink "for the road" and drives home. She lives about 10 minutes away.

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

But 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 DUI 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

experienced california attorneys can help with rising blood alcohol
An experienced DUI defense lawyer and expert witness can “back out” the driver's likely BAC at the time of driving.

6. How can a driver use "rising blood alcohol" to fight DUI charges?

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

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

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 the defendant 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: Bonnie went out for happy hour with her friends. Happy hour was between 6:00 and 7:00 P.M. The bartender remembers her ordering a mixed drink when she arrived and a shot during last call for happy hour.

A police officer stopped Bonnie at 7:20 PM. Bonnie agreed to a PAS breath test, which was given ten minutes later. It showed that Bonnie's BAC was at .08%. Based on the PAS test, the officer placed Bonnie under arrest.

At the station Bonnie elected a post-arrest DUI breath test. It showed a BAC of .09%. This is strong evidence that Bonnie's blood test was still rising when she drove. As a result, her BAC was likely below .08% when she was pulled over.

If Bonnie had kept driving, it is possible that she would have driven drunk. But the law does not punish what a driver might have done, only what he or she actually did. So unless there is evidence that Bonnie's driving was actually impaired, she should not be convicted of DUI.15

The expert's evidence can often get a case dismissed before trial

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 DUI plea bargain to a lesser charge.

But 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 the driver was over the legal limit (or even impaired) when he or she drove.

Charged with DUI in California? Call us for help…

rising blood alcohol california legal defense receptionists
Call us for help at 855-LAWFIRM

If you were arrested for driving under the influence in California, we invite you to contact us for a free consultation.

Call us at 855-LAWFIRM or submit the form on this page to speak to one of our experienced California drunk driving attorneys about your case.

We have local offices throughout California and practice in all California courts and DMV hearing offices.

We also have offices in Las Vegas and Reno that understand the rising blood alcohol defense in Nevada DUI cases.

Legal references:

  1. See, e.g., 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. See, e.g.,

  10. See e.g., 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, e.g., 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, e.g., 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, e.g., 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.”

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