No universal number of drinks causes a hangover as risk depends on genetics, biology, and drinking habits

Recent scientific research has made it clear that the question of how many alcoholic drinks will cause a hangover does not have a simple answer. The idea that there is a universal threshold for hangover risk is not supported by evidence. Instead, the likelihood and severity of a hangover depend on a complex mix of biological, genetic, and behavioral factors.

A hangover, known in medical terms as veisalgia, is a collection of symptoms that can include headache, fatigue, nausea, dizziness, sensitivity to light and sound, anxiety, and more. These symptoms usually begin several hours after drinking stops and peak when blood alcohol content returns to zero. The effects can last for 24 hours or longer and can significantly impair daily functioning.

One of the first challenges in understanding hangover risk is defining what counts as “a drink.” In the United States, a standard drink contains about 14 grams (0.6 fluid ounces) of pure alcohol. This is roughly equivalent to 12 ounces of regular beer at 5% alcohol by volume (ABV), 5 ounces of wine at 12% ABV, or 1.5 ounces of distilled spirits at 40% ABV. However, real-world servings often exceed these amounts. Craft beers may have higher ABV, wine pours are often larger than five ounces, and cocktails can contain multiple shots of liquor. This means that people often consume more alcohol than they realize.

The body’s reaction to alcohol involves several overlapping processes. Alcohol suppresses the hormone vasopressin, leading to increased urination and dehydration. This loss of fluids and electrolytes contributes to classic hangover symptoms like thirst, headache, and weakness. Alcohol also triggers an inflammatory response in the immune system, releasing cytokines that cause feelings of malaise and fatigue similar to being sick.

The digestive system is directly affected as well. Alcohol irritates the stomach lining and increases acid production, which can lead to nausea and vomiting. It also disrupts glucose metabolism in the liver, sometimes causing low blood sugar levels that result in shakiness and mood changes.

Alcohol’s impact on the brain is significant. While it may help people fall asleep faster, it disrupts sleep quality by reducing REM sleep and causing frequent awakenings. This leads to next-day grogginess and poor concentration. Alcohol also alters neurotransmitter levels in the brain; as its effects wear off, the brain rebounds into a state of hyperactivity that can cause anxiety and restlessness.

The process of breaking down alcohol in the liver produces acetaldehyde, a toxic compound much more harmful than ethanol itself. If drinking outpaces the liver’s ability to metabolize acetaldehyde into harmless acetate, this toxin builds up in the body and worsens hangover symptoms. Some alcoholic beverages contain additional compounds called congeners—byproducts of fermentation and distillation—that further increase hangover severity. Darker drinks like bourbon or brandy have higher congener content than clear spirits like vodka or gin.

Individual differences play a major role in hangover risk. Genetics account for up to half of the variation in how often people experience hangovers. Variations in genes that code for alcohol-metabolizing enzymes (ADH and ALDH) can make some people much more sensitive to alcohol’s toxic effects. For example, certain gene variants common among East Asians slow down acetaldehyde breakdown, leading to severe reactions even after small amounts of alcohol.

Other biological factors matter as well. Women generally have less body water than men and lower levels of stomach ADH enzyme, so they reach higher blood alcohol concentrations from the same amount of alcohol. Older adults may be more sensitive due to changes in body composition over time.

Psychological factors also influence hangover experiences. People with high levels of anxiety or negative emotions are more likely to report severe symptoms—a phenomenon sometimes called “hangxiety.” Guilt or regret about drinking can amplify physical discomfort.

Despite these non-modifiable risks, certain behaviors can reduce hangover likelihood and severity. Eating before or while drinking slows alcohol absorption by keeping it in the stomach longer; meals rich in protein, fat, and fiber are most effective for this purpose. Drinking slowly—no more than one standard drink per hour—gives the liver time to process alcohol without overwhelming its capacity.

Hydration is another key factor: alternating alcoholic drinks with water helps counteract dehydration and naturally slows consumption pace. Avoiding high-congener drinks like dark liquors or red wine can also help minimize symptoms.

Smoking while drinking increases hangover risk through combined negative effects on hydration, sleep quality, and immune function.

In summary, there is no single number of drinks that guarantees a hangover for everyone or anyone; risk depends on beverage type and strength, genetics, sex, age, body size and composition, psychological state, food intake, hydration status, pacing of consumption, sleep quality, and use of other substances like nicotine.

The best approach for those who wish to avoid or minimize hangovers is to understand their own risk profile based on these factors—and make informed choices about what they drink, how much they drink, how quickly they drink it, what they eat beforehand or during drinking sessions, how much water they consume alongside alcohol, whether they smoke while drinking, and how much rest they get afterward.

This evidence-based perspective moves beyond counting glasses toward a more nuanced understanding of personal limits and responsible consumption practices—empowering individuals to make decisions that protect their health and well-being after drinking occasions.