Blood Alcohol Concentration (BAC) measures the amount of alcohol in your bloodstream, expressed as a percentage. Many people mistakenly believe their BAC will drop quickly once they stop drinking, or that they can speed up the process. The body clears alcohol at a slow, predictable speed fixed by underlying physiology. This fixed rate of decline is why your BAC remains high long after your last drink.
Understanding Fixed Rate Metabolism
The liver eliminates over 90% of consumed alcohol using a specific enzyme system. Unlike the metabolism of food, alcohol elimination adheres to zero-order kinetics. This means the liver processes only a fixed, small amount of alcohol per hour, regardless of the current BAC level. The main enzyme, Alcohol Dehydrogenase (ADH), quickly becomes saturated and operates at its maximum capacity. For most moderate drinkers, this constant removal rate averages about 0.015% per hour.
The ADH enzyme converts ethanol into acetaldehyde, a toxic substance. A second enzyme, Aldehyde Dehydrogenase (ALDH), rapidly breaks acetaldehyde down into less harmful acetate. This two-step process has a bottleneck at the ADH step; once ADH is working as fast as it can, no additional alcohol will make it work faster. Time is the only factor that reduces your BAC.
Why Your BAC May Still Be Climbing
You may feel your intoxication increasing even after stopping because the absorption phase has not concluded. Alcohol moves from the stomach and small intestine into the bloodstream, a process that takes time. While elimination begins immediately, absorption often occurs much faster than the liver can eliminate the alcohol.
If you drank quickly or on a full stomach, alcohol may still be entering your bloodstream for an hour or more after your last sip. During this time, absorption can exceed the fixed rate of elimination, causing your BAC to continue rising or plateauing. Once absorption is complete, the steady, slow decline of the pure elimination phase begins.
Biological Factors That Affect Elimination Speed
Although the mechanism of elimination is fixed, the specific rate at which an individual processes alcohol varies based on several biological factors.
Body Composition
Body composition is a major variable, as alcohol distributes throughout total body water. A larger person with a higher percentage of body water will have a lower starting BAC for the same amount of alcohol consumed. Women generally have less body water and lower levels of stomach ADH, contributing to a higher BAC and sometimes a slightly slower elimination rate compared to men of similar size.
Genetics and Enzyme Efficiency
Genetic variations in ADH and ALDH enzymes dramatically affect metabolism speed. Certain genetic polymorphisms, prevalent in some East Asian populations, lead to a less efficient ALDH enzyme. This results in a buildup of toxic acetaldehyde and slower overall clearance. Conversely, chronic, heavy drinkers can temporarily develop an increased elimination rate, sometimes up to 0.030% per hour, due to the induction of the microsomal ethanol-oxidizing system (MEOS).
Food and Medication
Food in the stomach can influence the elimination rate. A substantial meal slows initial absorption but may also increase the liver’s blood flow, delivering alcohol to metabolizing enzymes more quickly. This increased blood flow can elevate the fixed elimination rate by 25% to 50% temporarily. Certain medications, such as acetaminophen, can interact with liver enzymes, potentially slowing the overall metabolic speed.
Debunking Myths About Acceleration
Since alcohol elimination is governed by zero-order kinetics, no common home remedy can accelerate the chemical breakdown of alcohol in the liver. Methods like drinking black coffee, taking a cold shower, or intense exercise only affect the perception of impairment, not the actual BAC. Caffeine may make you feel more alert, but the concentration of alcohol in your blood remains unchanged.
Exercising or sweating excretes only a negligible amount of alcohol, as 92% to 98% must be processed by the liver. Hydration helps mitigate dehydration and side effects but does not enhance the speed of the ADH enzyme. The liver must take its fixed amount of time to process the alcohol molecules, meaning patience is the only way to return your BAC to zero.