Hangover Science By Hungover Australia

The Science of Hangovers: What Actually Happens to Your Body

A deep dive into the biology behind hangovers -- from acetaldehyde toxicity and dehydration to inflammation and genetics. Understand why you feel so rough and what science says about it.

We have all been there. You wake up with a pounding headache, a churning stomach, and a sincere promise to yourself that you will never drink again. But what is actually going on inside your body when you are hungover? Understanding the science can help you make better choices — both about how much you drink and how you recover.

Let’s break down what happens from the moment alcohol enters your system to the miserable morning after.

How Your Body Processes Alcohol

Before we can understand hangovers, we need to understand how your liver handles alcohol. When you have a drink, your body treats ethanol (the active ingredient in alcoholic beverages) as a toxin and prioritises breaking it down.

The Two-Step Breakdown

Your liver metabolises alcohol in two main stages:

  1. Ethanol to acetaldehyde. An enzyme called alcohol dehydrogenase (ADH) converts ethanol into acetaldehyde — a highly toxic compound that is between 10 and 30 times more toxic than alcohol itself.

  2. Acetaldehyde to acetate. A second enzyme, aldehyde dehydrogenase (ALDH2), then converts acetaldehyde into acetate, a relatively harmless substance your body can use for energy or excrete.

The problem is that your liver can only process roughly one standard drink per hour. When you drink faster than that, acetaldehyde builds up in your bloodstream, and that is when the trouble really starts.

Why Acetaldehyde Is the Main Villain

Acetaldehyde is responsible for many of the classic hangover symptoms. It triggers inflammation throughout your body, damages cell membranes, and irritates the lining of your stomach and intestines. Research published in Alcohol and Alcoholism has confirmed that elevated acetaldehyde levels correlate directly with hangover severity.

Think of it this way: your liver is running a detoxification assembly line, and when you overload it, the half-processed toxic waste backs up into the rest of your system.

Dehydration: More Than Just Being Thirsty

One of the most well-known effects of alcohol is dehydration, but the mechanism is more nuanced than most people realise.

How Alcohol Dehydrates You

Alcohol suppresses the release of vasopressin (also called antidiuretic hormone or ADH — not to be confused with the liver enzyme). Vasopressin normally tells your kidneys to reabsorb water. Without it, your kidneys send that water straight to your bladder instead.

This is why you need to visit the bathroom so frequently when you are drinking. For every standard drink you consume, your body can expel up to 120 millilitres more urine than the volume of the drink itself. Over a big night, that adds up to a significant fluid deficit.

The Consequences of Dehydration

Dehydration contributes to several hangover symptoms:

  • Headaches. Your brain is about 75 per cent water. When you are dehydrated, your brain can temporarily shrink and pull away from the skull, triggering pain receptors in the surrounding membrane. This is the mechanical basis for that splitting hangover headache.
  • Dry mouth and thirst. Your salivary glands need adequate hydration to function, and your body’s thirst signals go into overdrive.
  • Fatigue and dizziness. Reduced blood volume means less oxygen delivery to your muscles and brain.
  • Electrolyte imbalance. Along with water, you lose essential minerals like sodium, potassium, and magnesium — all of which are crucial for normal muscle and nerve function.

The Inflammatory Response

A hangover is, in many ways, an inflammatory event. Research from Kyungpook National University in South Korea found that hangover severity correlates strongly with elevated levels of inflammatory markers in the blood, including cytokines like interleukin-10, interleukin-12, and interferon-gamma.

What Triggers the Inflammation

Several factors drive the inflammatory cascade:

  • Acetaldehyde damage. As discussed, this toxic metabolite directly damages tissues and triggers your immune system to respond.
  • Gut permeability. Alcohol increases the permeability of your intestinal lining (sometimes called “leaky gut”), allowing bacterial endotoxins to enter your bloodstream. Your immune system reacts to these endotoxins with a full inflammatory response.
  • Oxidative stress. Alcohol metabolism generates free radicals — unstable molecules that damage cells and DNA. Your body’s antioxidant defences become overwhelmed, leading to oxidative stress.

Why You Feel Like You Have the Flu

The inflammatory cytokines released during a hangover are the same molecules your body produces when you are fighting an infection. That is why a bad hangover can feel remarkably similar to having the flu: body aches, fatigue, brain fog, nausea, and a general sense of malaise are all driven by your immune system’s inflammatory response rather than the alcohol itself.

Your Immune System Takes a Hit

Beyond the inflammatory response, alcohol directly suppresses your immune system. Research has shown that even a single episode of heavy drinking can reduce the activity of natural killer cells and alter cytokine production for up to 24 hours afterwards.

This immune suppression is one reason why you might feel run-down or catch a cold in the days following a big night out. Your body is simultaneously trying to recover from the toxic effects of alcohol while operating with compromised defences.

Electrolyte Imbalance: The Hidden Problem

While dehydration gets most of the attention, electrolyte imbalance is arguably just as important to how awful you feel.

Key Electrolytes Affected

  • Potassium. Essential for heart rhythm, muscle contraction, and nerve signalling. Low potassium contributes to muscle weakness, cramps, and fatigue.
  • Magnesium. Involved in over 300 enzymatic reactions in your body. Depletion leads to headaches, muscle tension, irritability, and poor sleep quality.
  • Sodium. Critical for fluid balance and nerve function. Loss contributes to dizziness, confusion, and nausea.
  • Zinc. Important for immune function and enzyme activity. Even moderate drinking depletes zinc stores.

Replenishing these electrolytes — not just water — is a key part of hangover recovery, which is why plain water alone often does not make you feel much better.

Congeners: Why Some Drinks Hit Harder

Not all alcoholic drinks produce equally bad hangovers, and the reason comes down to congeners.

What Are Congeners?

Congeners are biologically active compounds produced during the fermentation and ageing process. They include substances like methanol, tannins, fusel oils, and various aldehydes. While they contribute to the flavour, aroma, and colour of alcoholic beverages, they also add to the toxic burden your body must process.

High-Congener vs Low-Congener Drinks

Research published in Current Drug Abuse Reviews confirmed that high-congener drinks produce significantly worse hangovers than low-congener alternatives at the same blood alcohol level.

High-congener drinks (worse hangovers):

  • Bourbon and whiskey
  • Red wine
  • Brandy and cognac
  • Dark rum
  • Tequila (especially gold varieties)

Low-congener drinks (comparatively milder hangovers):

  • Vodka
  • White wine
  • Gin
  • Light rum
  • Light-coloured beer

This does not mean low-congener drinks are “safe” — they still cause hangovers through all the other mechanisms described here. But if you are comparing like for like, a night on bourbon will generally leave you feeling worse than a night on vodka.

Sleep Disruption: Why You Wake Up Exhausted

You might think alcohol helps you sleep — after all, it can make you feel drowsy. But alcohol is actually one of the worst things for sleep quality.

How Alcohol Wrecks Your Sleep

  • REM suppression. Alcohol significantly reduces the amount of REM (rapid eye movement) sleep you get. REM sleep is critical for memory consolidation, emotional regulation, and feeling rested.
  • Sleep fragmentation. As your blood alcohol level drops during the night, you experience a “rebound” effect that causes frequent awakenings, often in the second half of the night.
  • Breathing disruption. Alcohol relaxes the muscles in your throat, which can worsen snoring and sleep apnoea, further reducing sleep quality.
  • Early waking. Many drinkers find themselves wide awake at 4 or 5 am, unable to get back to sleep. This is partly due to the rebound effect and partly due to drops in blood sugar.

Even if you were in bed for eight hours, the quality of sleep you got after drinking heavily might be equivalent to only four or five hours of proper rest. This sleep debt compounds the fatigue, brain fog, and irritability of the hangover itself.

Stomach Irritation and Nausea

That queasy, unsettled stomach is not just in your head — alcohol directly irritates the lining of your gastrointestinal tract.

The Mechanisms

  • Increased acid production. Alcohol stimulates your stomach to produce more hydrochloric acid, which can irritate the stomach lining and contribute to nausea and reflux.
  • Delayed gastric emptying. Alcohol slows the movement of food through your digestive system, leading to that heavy, bloated feeling.
  • Mucosal damage. Concentrated alcohol can physically damage the protective mucous layer of your stomach, leading to inflammation (gastritis).
  • Gut motility changes. Alcohol can cause both constipation and diarrhoea by disrupting normal gut motility patterns.

Why Some People Get Worse Hangovers

If you have ever wondered why your mate can drink the same amount as you and bounce out of bed the next morning while you are incapacitated, genetics plays a significant role.

The Genetics of Alcohol Metabolism

The efficiency of your ADH and ALDH2 enzymes is largely determined by your genes.

  • ALDH2 deficiency. Approximately 36 per cent of East Asian populations carry a variant of the ALDH2 gene (called ALDH2*2) that makes the enzyme significantly less effective. People with this variant accumulate acetaldehyde much more rapidly, leading to facial flushing, nausea, and dramatically worse hangovers. This is commonly known as “Asian flush” or “alcohol flush reaction.”
  • ADH variants. Some people have more active forms of ADH, meaning they convert ethanol to acetaldehyde faster than their ALDH2 can clear it. This creates a toxic bottleneck.
  • Cytokine response. Genetic variation in inflammatory cytokine production means some people mount a much stronger immune response to the same amount of alcohol.

Other Factors That Influence Hangover Severity

Beyond genetics, several other variables matter:

  • Age. Hangovers tend to worsen as you get older. Liver enzyme efficiency declines, and your body becomes less resilient to oxidative stress and dehydration.
  • Sex. Women tend to experience worse hangovers than men at the same consumption level, partly because women generally have less body water (and therefore achieve higher blood alcohol concentrations) and produce less ADH in the stomach lining.
  • Body composition. Higher body fat percentage means less water to dilute alcohol, leading to higher blood alcohol levels.
  • Hydration status. If you were already dehydrated before drinking (common in the Australian climate), your hangover will likely be worse.
  • Food intake. Drinking on an empty stomach leads to faster alcohol absorption and worse outcomes.
  • Medications. Certain medications, including common over-the-counter painkillers, can interact with alcohol and worsen hangover symptoms.
  • Sleep quality. If your sleep was already poor before the drinking session, the compounding effect will be significant.

A Note on “Hangxiety”

Many people experience significant anxiety during a hangover — a phenomenon sometimes called “hangxiety.” This is not imaginary. Alcohol initially boosts the activity of GABA (your brain’s primary calming neurotransmitter) and suppresses glutamate (an excitatory neurotransmitter). When the alcohol wears off, your brain rebounds in the opposite direction: GABA activity drops and glutamate surges, creating a neurochemical state that is primed for anxiety, restlessness, and irritability.

If you already experience anxiety, hangovers can be particularly distressing. This is worth keeping in mind when making decisions about how much to drink.

The Hormonal Cascade: Beyond Neurotransmitters

While the neurotransmitter changes in hangovers are well documented, alcohol also triggers significant hormonal disruptions that contribute to how awful you feel.

Cortisol and the Stress Response

Alcohol activates your hypothalamic-pituitary-adrenal (HPA) axis — the central command system for your body’s stress response. During and after heavy drinking, your cortisol levels rise substantially. Research published in Psychopharmacology has shown that cortisol levels during a hangover can be comparable to those experienced during moderate psychological stress.

This cortisol surge contributes to the anxiety, irritability, and general sense of unease that characterise a hangover. It also impairs immune function and disrupts blood sugar regulation, compounding other hangover mechanisms. In people with pre-existing anxiety disorders, this cortisol spike can trigger particularly distressing symptoms — a phenomenon increasingly known as “hangxiety.”

Insulin and Blood Sugar Dysregulation

Alcohol has a complex relationship with blood sugar. While drinking, your liver prioritises alcohol metabolism over glucose production (a process called gluconeogenesis). This can cause your blood sugar to drop, particularly if you have not eaten. The result is hypoglycaemia — characterised by shakiness, weakness, sweating, confusion, and irritability.

At the same time, the sugary mixers in many popular drinks (soft drinks, juice, pre-mixed cocktails) can cause sharp blood sugar spikes. The net effect is a rollercoaster of glucose highs and lows that continues into the hangover period. This blood sugar instability is a significant contributor to hangover fatigue, brain fog, and mood disturbance.

Vasopressin Suppression and Water Balance

As discussed in the dehydration section, alcohol suppresses vasopressin (antidiuretic hormone), leading to excessive urination. But the hormonal effects extend further. Vasopressin also plays a role in blood pressure regulation and social bonding behaviour. Its suppression during heavy drinking may partly explain the emotional volatility and social anxiety many people experience during hangovers.

The Role of Oxidative Stress in Hangover Damage

Oxidative stress is one of the less discussed but scientifically important mechanisms underlying hangovers. When your liver processes alcohol, the metabolic reactions generate reactive oxygen species (ROS) — unstable molecules commonly known as free radicals.

How Free Radicals Cause Damage

Free radicals are missing an electron and will steal electrons from nearby molecules to stabilise themselves, damaging those molecules in the process. This chain reaction can damage:

  • Cell membranes: Leading to impaired cellular function and inflammation
  • Proteins: Disrupting enzyme activity and structural integrity
  • DNA: Potentially contributing to long-term cellular damage with repeated heavy drinking

Your body has natural antioxidant defences — primarily glutathione, superoxide dismutase, and catalase — but heavy drinking can overwhelm these systems. When antioxidant capacity is exceeded, oxidative stress occurs, and the resulting damage contributes to the systemic inflammation, fatigue, and malaise of a hangover.

Glutathione Depletion

Glutathione is your body’s master antioxidant and plays a critical role in detoxifying acetaldehyde. Each molecule of acetaldehyde that your liver neutralises requires glutathione. During heavy drinking, your glutathione stores can become significantly depleted, leaving your cells more vulnerable to oxidative damage.

This is one reason why hangovers tend to be worse when you drink on an empty stomach or when you are already nutritionally depleted. Foods rich in cysteine (such as eggs, poultry, and dairy) provide the building blocks for glutathione synthesis and may support recovery.

Hangovers and the Cardiovascular System

Alcohol’s effects on your heart and blood vessels are another piece of the hangover puzzle that deserves attention.

Heart Rate and Rhythm Changes

During a hangover, many people notice a faster-than-normal heart rate (tachycardia). This is driven by multiple factors: dehydration reduces blood volume, forcing the heart to pump faster to maintain blood pressure; the sympathetic nervous system is activated as part of the rebound excitability following alcohol’s sedative effects; and elevated cortisol and noradrenaline further increase heart rate.

In some cases, heavy drinking can trigger temporary heart rhythm abnormalities — a phenomenon sometimes called “holiday heart syndrome” because it tends to present after periods of heavy social drinking. While usually self-limiting, it can be alarming and occasionally requires medical attention.

Blood Pressure Fluctuations

Alcohol initially causes blood vessels to dilate (vasodilation), which is why you might feel warm and flushed while drinking. During the hangover period, blood vessels can constrict as your body rebounds from this effect, contributing to headaches and feelings of tightness or pressure. These blood pressure fluctuations are also partly responsible for the dizziness many people experience when standing up during a hangover (orthostatic hypotension).

The Timeline of a Hangover: What Happens Hour by Hour

Understanding the typical progression of a hangover can help contextualise what your body is going through at each stage.

Hours 0 to 6 (Still Drinking and Immediate Aftermath)

While you are still drinking, your blood alcohol concentration (BAC) is rising. Acetaldehyde is accumulating faster than your liver can clear it. You are losing fluid and electrolytes through increased urination. Your stomach lining is becoming progressively more irritated. Despite all this, the sedative effects of alcohol are masking many of the symptoms.

Hours 6 to 12 (Peak Hangover)

This is typically when hangover symptoms are at their worst. Your BAC has dropped to near zero, but the damage is done. Acetaldehyde levels may still be elevated. Your body is dehydrated and electrolyte-depleted. The inflammatory cytokine response is in full swing. Your neurotransmitter systems are in rebound — GABA is underperforming while glutamate is in overdrive. Sleep, if you managed it, was fragmented and lacked restorative REM phases.

Hours 12 to 24 (Gradual Recovery)

Your liver has cleared most of the toxic metabolites. Rehydration and electrolyte replacement are beginning to take effect. Inflammatory markers are declining. Neurotransmitter balance is slowly restoring. Most people notice a gradual improvement during this phase, though fatigue and low mood may persist.

Hours 24 to 48 (Resolution)

For most moderate hangovers, symptoms have largely resolved by this point. However, after particularly heavy drinking sessions, residual effects — especially fatigue, brain fog, and mood disturbance — can persist for up to 72 hours. Sleep quality may take an additional night or two to fully normalise.

Australian Research Into Hangover Science

Australia has contributed significantly to our scientific understanding of alcohol’s effects on the body, and several Australian research institutions are at the forefront of hangover research.

The Swinburne University Alcohol Research Group

Researchers at Swinburne University of Technology in Melbourne have published extensively on the cognitive effects of hangovers, including their impact on driving ability, workplace performance, and decision-making. Their work has demonstrated that hangover-related cognitive impairment can be comparable to being at the legal blood alcohol limit — even when BAC has returned to zero.

NHMRC Guidelines and Their Evidence Base

The National Health and Medical Research Council’s 2020 guidelines on alcohol consumption were informed by comprehensive reviews of the global evidence on alcohol and health. The recommendation of no more than 10 standard drinks per week and no more than 4 on any single occasion represents the NHMRC’s assessment of the threshold at which alcohol-related health risks begin to increase meaningfully. These guidelines are among the most conservative in the world, reflecting Australia’s commitment to evidence-based public health policy.

The CSIRO and Gut Health Research

CSIRO researchers have contributed to our understanding of how alcohol affects the gut microbiome — the community of trillions of bacteria in your digestive system. Their work has shown that heavy drinking disrupts microbial diversity and can promote the growth of harmful bacterial species, contributing to gut inflammation and the “leaky gut” phenomenon that drives systemic inflammation during hangovers.

Frequently Asked Questions

Why do hangovers get worse as you age?

Several physiological changes contribute to worsening hangovers with age. Liver enzyme efficiency declines, meaning your body is slower to clear acetaldehyde. Total body water decreases (particularly after age 40), resulting in higher blood alcohol concentrations from the same intake. Your antioxidant defences become less robust, increasing vulnerability to oxidative stress. And your ability to recover from disrupted sleep diminishes. Additionally, many older adults take medications that interact with alcohol, compounding hangover symptoms.

Is there a genetic test to determine how bad my hangovers will be?

Commercial genetic tests can identify variants in the ADH and ALDH2 genes, which influence alcohol metabolism speed and acetaldehyde clearance. The ALDH2*2 variant, common in people of East Asian descent, is the most well-characterised. However, hangover severity is influenced by many factors beyond these two genes — including inflammatory cytokine production, sleep quality, gut microbiome composition, and drinking behaviour — so a genetic test alone cannot fully predict your hangover experience.

Can regular heavy drinking permanently change how your body handles alcohol?

Yes. Chronic heavy drinking causes adaptive changes in liver enzyme activity, neurotransmitter receptor density, and immune function. Tolerance develops — meaning you need more alcohol to achieve the same effects — but this does not mean your body is handling alcohol better. In fact, the opposite is true: the metabolic burden increases, and cumulative damage to the liver, brain, and cardiovascular system accumulates over time. If you find you need significantly more alcohol to get drunk than you used to, this is a warning sign that warrants a conversation with your GP.

Do women really get worse hangovers than men?

On average, yes. Women tend to have higher body fat percentages and lower total body water than men of the same weight, meaning alcohol is distributed in a smaller volume of water and produces higher blood alcohol concentrations. Women also produce less gastric ADH (the form of the enzyme in the stomach lining that begins breaking down alcohol before it reaches the bloodstream), further increasing BAC. Hormonal fluctuations across the menstrual cycle can also influence hangover severity, with some women reporting worse symptoms during the luteal phase.

Does mixing different types of alcohol actually make hangovers worse?

The common advice of “beer before wine, you’ll feel fine; wine before beer, you’ll feel queer” has been tested in a controlled trial published in the American Journal of Clinical Nutrition in 2019. The researchers found no significant difference in hangover severity based on the order of drinks consumed. What matters is the total amount of alcohol consumed, not the sequence or combination. However, mixing drinks can make it harder to track your total intake, which indirectly leads to heavier consumption and worse hangovers.

The Bottom Line

A hangover is not a single event but a complex, multi-system response involving:

  • Toxic acetaldehyde accumulation
  • Dehydration and electrolyte depletion
  • Systemic inflammation and immune activation
  • Sleep disruption and neurotransmitter imbalance
  • Gastrointestinal irritation
  • Oxidative stress
  • Hormonal disruption and blood sugar instability
  • Cardiovascular stress

Understanding these mechanisms can help you make informed decisions about drinking and recovery. The most effective way to prevent a hangover is, of course, to drink less or not at all. But when you do choose to drink, pacing yourself, staying hydrated, eating beforehand, and choosing lower-congener drinks can all reduce the severity of what follows.

If you or someone you know is struggling with alcohol use, the National Alcohol and Other Drug Hotline is available 24 hours a day on 1800 250 015. It is free, confidential, and staffed by trained counsellors.

Health Disclaimer: This article is for informational purposes only and does not constitute medical advice. The content is based on published scientific research but should not be used as a substitute for professional medical guidance. If you have concerns about your health or alcohol consumption, please consult a qualified healthcare professional. If you are experiencing a medical emergency, call 000 immediately.