A single shot of vodka represents a fixed measure of alcohol that initiates a sequence of physiological responses in the body. Whether a single shot has a noticeable effect depends on an individual’s unique biology and external circumstances. The impact is always present at a measurable, cellular level, even if the person consuming it does not perceive any change. The physical and legal consequences of one drink are rooted in the science of how the body handles alcohol.
Defining the Standard Shot
The impact of one shot is defined by its precise alcohol content. In the United States, a standard drink contains 0.6 ounces, or approximately 14 grams, of pure ethanol. A standard shot of distilled spirits like vodka is typically measured as 1.5 fluid ounces (about 44 milliliters).
This 1.5-ounce volume is based on a standard alcohol concentration of 40% Alcohol by Volume (ABV), or 80 proof. One standard shot of vodka is considered one standard drink because it contains the defined amount of pure alcohol. This quantifiable measure is the starting point for calculating the subsequent Blood Alcohol Concentration (BAC) and predicting the physical effects.
Immediate Physiological Response
Once swallowed, the ethanol in the vodka does not require digestion and begins absorbing into the bloodstream almost immediately. Roughly 20% of the alcohol is absorbed through the stomach lining, while the remaining 80% passes into the small intestine for rapid uptake. The alcohol then travels via the bloodstream to the liver, heart, lungs, and the brain.
The Blood Alcohol Concentration (BAC) starts to rise within minutes. For an average person consuming one shot on an empty stomach, the peak BAC can reach between 0.01% and 0.03% within the first hour. At this low concentration, alcohol acts as a central nervous system depressant by subtly affecting neurochemistry. Ethanol enhances the activity of Gamma-aminobutyric acid (GABA) receptors, the brain’s primary inhibitory neurotransmitters.
This minor increase in GABA activity slows down communication between neurons, which can lead to the first, barely perceptible changes in the body. These initial effects at a BAC of 0.02% may include a slight feeling of muscle relaxation, an altered or slightly elevated mood, and a small decline in visual function or judgment. The heart rate may also be affected, as GABAergic activity plays a role in cardiovascular regulation within the brain.
Factors Influencing Absorption and Metabolism
The actual peak BAC and the subjective feeling of the one shot are influenced by several individual factors. Body composition is a primary determinant because alcohol is highly soluble in water but not fat. Since women typically have a lower percentage of total body water (45% to 50%) compared to men (55% to 65%), the same amount of alcohol is less diluted, resulting in a higher BAC.
Biological sex also plays a role in metabolism due to the enzyme alcohol dehydrogenase (ADH), which breaks down alcohol in the stomach. Women generally have lower levels of this gastric enzyme activity than men, allowing more alcohol to pass directly into circulation. The presence of food in the stomach is another significant factor, as a substantial meal slows gastric emptying, delaying the passage of alcohol into the small intestine. Drinking a single shot with a meal can reduce the peak BAC level by up to 40% compared to consuming it on an empty stomach.
Relating One Shot to Legal Thresholds
The resulting BAC from a single shot has legal implications, particularly regarding the threshold for Driving Under the Influence (DUI). In most US jurisdictions, the legal limit for operating a motor vehicle is a BAC of 0.08%. For an average-sized adult male weighing about 150 pounds, one standard shot consumed quickly will typically result in a BAC of approximately 0.02% to 0.03%.
A smaller individual, such as a 100-pound person, may reach a BAC closer to 0.04% after one shot, especially if they have an empty stomach. Although a single shot generally keeps an average person below the 0.08% legal limit, impairment begins with the first drink. Even at 0.02% BAC, some individuals experience a measurable decline in visual function, judgment, and the ability to multitask.