Ethanol is the molecule in alcoholic drinks that gets you drunk. It’s a simple compound made of just two carbon atoms bonded to a hydroxyl group, and it’s the only type of alcohol humans can drink without it being lethal. Whether you’re sipping beer, wine, or spirits, ethanol is the single active ingredient responsible for intoxication. A standard drink in the United States contains about 14 grams of pure ethanol, roughly 0.6 fluid ounces.
How Ethanol Reaches Your Brain
Ethanol is a small, water-soluble molecule, which is exactly why it moves through your body so efficiently. After you swallow a drink, some ethanol absorbs slowly through the stomach lining, but the majority passes into the small intestine, where absorption speeds up considerably. From there it enters your bloodstream and distributes freely throughout most of your body’s water content. It does not absorb well into fat tissue, which is one reason body composition affects how drunk you feel.
Several factors change how quickly ethanol hits your bloodstream. Drinking on an empty stomach produces the fastest spike in blood alcohol levels. Food, especially carbohydrates, slows gastric emptying and can reduce peak blood alcohol concentration to roughly a quarter of what it would be without food. Carbonated mixers like soda or tonic water speed things up by pushing alcohol through the stomach faster. Drinks around 20% alcohol by volume (like sherry or port) tend to produce the quickest rise in blood alcohol, while stronger spirits at 40% can actually slow absorption by delaying gastric emptying.
What Ethanol Does Inside Your Brain
Once ethanol crosses into the brain, it works on two major signaling systems simultaneously. Your brain has a constant push-and-pull between signals that excite neurons and signals that calm them down. Ethanol tips this balance heavily toward the “calm down” side, which is why alcohol is classified as a central nervous system depressant.
The calming side involves a neurotransmitter called GABA, which normally tells neurons to slow their activity. Ethanol amplifies GABA’s effect by making its receptors open more frequently, stay open longer, and spend less time in a closed state. The result is a flood of inhibitory signaling: your reaction time drops, your muscles relax, your speech starts to slur, and your judgment loosens. At the same time, ethanol blocks receptors for glutamate, the brain’s primary excitatory neurotransmitter. With the “speed up” signal suppressed and the “slow down” signal boosted, your brain enters the blunted, disinhibited state you experience as being drunk.
There’s also a reward component. At lower concentrations, ethanol triggers the release of dopamine in the brain’s reward center by activating specialized neurons in a region called the nucleus accumbens. This dopamine surge is responsible for the initial euphoria and warmth you feel after the first drink or two. Interestingly, this effect is strongest at lower blood alcohol levels and diminishes as concentration rises, which helps explain why the first drink often feels the best.
How Your Body Breaks Ethanol Down
Your liver does most of the work. An enzyme called alcohol dehydrogenase (ADH) converts ethanol into acetaldehyde, a toxic compound and known carcinogen. Under normal circumstances, acetaldehyde doesn’t linger long. A second enzyme, aldehyde dehydrogenase (ALDH), quickly converts it into acetate, a relatively harmless substance your body then breaks down into water and carbon dioxide.
The speed of this two-step process determines how long you stay intoxicated. Your liver can only process a limited amount of ethanol per hour, which is why drinking faster than your liver can keep up causes blood alcohol levels to climb. A backup enzyme system involving a protein called CYP2E1 also helps break down ethanol, but it plays a smaller role under normal drinking conditions.
Why Some People React Differently
Genetics play a significant role in how ethanol affects you. Roughly 540 million people worldwide carry a genetic variant in the ALDH enzyme called ALDH2*2, which makes the enzyme inactive or much less efficient. When these individuals drink, acetaldehyde builds up in their system instead of being quickly cleared. The result is the alcohol flush response: facial reddening, a racing heart, nausea, and general discomfort after even small amounts of alcohol. This variant is most common among people of East Asian descent.
Beyond genetics, your sex, body size, body composition, hormonal cycle, and drinking history all influence how the same amount of ethanol affects you. People with more body water (typically those with larger, more muscular frames) dilute ethanol more effectively, resulting in lower blood alcohol concentrations from the same number of drinks. Women tend to reach higher blood alcohol levels than men of the same weight, partly due to differences in body water percentage and enzyme activity.
Do Other Ingredients in Drinks Matter?
Alcoholic beverages contain more than just ethanol and water. Compounds called congeners form during fermentation and aging. These include acetone, tannins, fusel oils, and small amounts of methanol. Darker spirits like bourbon contain roughly 37 times more congeners than clear spirits like vodka.
Despite what many people believe, congeners don’t significantly change how drunk you get. Studies comparing bourbon and vodka at equivalent ethanol doses found no meaningful difference in acute impairment, sleep quality, or cognitive performance. What congeners do affect is how you feel the next morning. Bourbon consistently produced worse hangovers than vodka in controlled research, even when the ethanol dose was identical. So while ethanol alone drives intoxication, the other molecules in your drink can make the aftermath considerably worse.
The bottom line is straightforward: ethanol is the one molecule doing the heavy lifting. Everything else in your glass, from the congeners to the flavorings to the carbonation, only modifies how fast the ethanol gets absorbed or how rough you feel the next day. The drunk part is all ethanol.