Drinking alcohol is ethanol, a simple molecule made of two carbon atoms, six hydrogen atoms, and one oxygen atom. It’s produced when yeast feeds on sugars and, through fermentation, converts them into ethanol and carbon dioxide. Among the many types of alcohol that exist in chemistry, ethanol is the only one safe enough for human consumption, and even then, “safe” comes with significant caveats. Every alcoholic beverage, from light beer to cask-strength whiskey, contains this same molecule at varying concentrations.
How Alcohol Is Made
All alcoholic beverages start with fermentation. Yeast breaks down sugars from a raw ingredient (grapes, barley, rice, agave, or dozens of others) and produces ethanol as a byproduct. The process typically yields a liquid with roughly 5 to 10 percent alcohol, which is why beer and wine naturally land in that range.
To make spirits like vodka, rum, or whiskey, that fermented liquid goes through distillation. The mixture is heated until the ethanol evaporates (it boils at a lower temperature than water), then the vapor is captured and cooled back into liquid form. Each round of evaporation and re-condensation increases the alcohol concentration, which is how distilled spirits reach 40 percent alcohol or higher. The choice of raw ingredient, yeast strain, aging process, and distillation method is what gives each beverage its distinct flavor.
What Happens When You Drink It
Alcohol is absorbed slowly through the stomach and rapidly through the small intestine. How fast it reaches your bloodstream depends largely on how quickly your stomach empties. Drinking on an empty stomach means the ethanol passes into the small intestine faster, producing a quicker and higher peak in blood alcohol concentration. Food in the stomach slows that process down, which is why eating before or while drinking blunts the effects.
Once absorbed, ethanol travels through the bloodstream to every organ in the body, including the brain. Your liver handles most of the breakdown. An enzyme converts ethanol into a toxic intermediate compound called acetaldehyde, which is a known carcinogen. A second enzyme then converts acetaldehyde into acetate, which the body can break down into water and carbon dioxide and eliminate. This two-step process is the bottleneck: your liver can only work so fast, which is why drinking faster than your body can metabolize leads to rising blood alcohol levels.
How It Affects Your Brain
Alcohol’s effects on mood, coordination, and judgment come from the way it interacts with two key signaling systems in the brain. It boosts the activity of GABA, the brain’s primary “slow down” signal, both by increasing the release of GABA and by making the receiving cells more responsive to it. At the same time, it suppresses glutamate, the brain’s main “speed up” signal. The combined result is a nervous system that’s running on the brakes with the accelerator cut. That’s why alcohol causes relaxation, slowed reflexes, impaired judgment, and, at high enough doses, unconsciousness.
With chronic, heavy drinking, the brain adapts to this altered chemical environment. It dials down GABA sensitivity and ramps up glutamate activity to compensate. This is the basis of tolerance (needing more to feel the same effect) and also why alcohol withdrawal can be dangerous: remove the alcohol suddenly, and the brain is left in a hyper-excitable state without its usual dampener.
Impairment at Different Levels
Blood alcohol concentration (BAC) is measured as a percentage. According to the National Highway Traffic Safety Administration, impairment begins well before you’d feel “drunk.”
- 0.02 BAC: Some loss of judgment, slight body warmth, altered mood. Your ability to track moving objects and divide attention between tasks starts to decline.
- 0.05 BAC: Exaggerated behavior, lowered alertness, reduced coordination. Small-muscle control slips, making it harder to focus your eyes. Steering becomes more difficult.
- 0.08 BAC: The legal limit for driving in most U.S. states. Balance, speech, vision, and reaction time are all measurably impaired. Short-term memory, self-control, and the ability to detect danger deteriorate.
- 0.10 BAC: Clear deterioration of reaction time. Slurred speech, poor coordination, slowed thinking.
- 0.15 BAC: Far less muscle control than normal, significant loss of balance, and vomiting is common unless tolerance has built up over time.
Calories and Energy
Pure ethanol contains about 7.1 calories per gram, placing it between fat (9 calories per gram) and carbohydrates or protein (4 calories per gram). A standard glass of wine or pint of beer carries roughly 120 to 180 calories, much of which comes from the alcohol itself rather than the sugars.
Your body doesn’t store ethanol the way it stores fat or carbohydrates. Instead, it treats alcohol as a priority fuel and burns it first, pushing the metabolism of other nutrients to the back of the line. This is one reason heavy drinking contributes to weight gain: while your liver is busy processing ethanol, the calories from the food you ate alongside it are more likely to end up stored as fat. There’s also evidence that at higher intakes, some of the energy from ethanol is simply lost as heat rather than used productively by the body, so the effective calorie count may be lower than the theoretical 7.1 figure. Still, the calories add up, especially with regular drinking.
Long-Term Effects on the Body
The liver takes the heaviest hit from prolonged alcohol use because it’s the organ doing most of the metabolic work. Years of heavy drinking can cause the liver to become inflamed and eventually scarred, a condition called cirrhosis. Once scarring is advanced, the damage is largely irreversible.
The heart and brain are also vulnerable. People who abuse alcohol have significantly higher rates of cardiovascular disease, including a form of heart muscle damage specific to chronic drinkers. In the brain, alcohol promotes persistent inflammation that leads to the death of nerve cells over time. Postmortem studies of people with long histories of heavy drinking show measurable degeneration in brain tissue, which correlates with the cognitive decline, memory problems, and mood disturbances often seen in chronic alcohol use.
No Universally “Safe” Amount
The World Health Organization’s position is straightforward: because any alcohol use carries some short-term and long-term health risks, it’s difficult to define a universally safe threshold. Even the concept of a “standard drink” varies by country. In the United Kingdom, a standard drink contains 8 grams of pure ethanol, while in the United States it’s 14 grams, nearly double. This inconsistency means that guidelines about “moderate drinking” can mean very different things depending on where you live.
What’s clear from the evidence is that risk increases with the amount consumed. Light, occasional drinking carries a much smaller risk profile than regular heavy drinking, but zero alcohol is the only level that carries zero alcohol-related risk. How you weigh that against the social and personal enjoyment of drinking is an individual decision, but it helps to make it with accurate information about what the substance actually does once it’s in your body.