How long does a hangover last? The science explained
You wake up with a pounding head, a churning stomach and one question: when will this end? For most people the answer is up to 24 hours — but why it lasts that long, and why some hangovers are so much worse than others, comes down to some surprisingly messy biology.
The short answer: up to 24 hours
According to the US National Institute on Alcohol Abuse and Alcoholism (NIAAA), hangover symptoms can last 24 hours or longer. Counterintuitively, a hangover doesn't peak while you're drinking or even just after — it typically peaks when your blood alcohol concentration (BAC) falls back to around zero, which for most people is the morning after.
That's why you can go to bed feeling merely tired and wake up feeling far worse. Your body has spent the night processing the alcohol, and the hangover is what's left behind once the job is done: inflammation, dehydration, disrupted sleep and a build-up of by-products your system is still mopping up.
What actually causes a hangover?
There's no single culprit. Research points to several overlapping processes, which is part of why no "cure" has ever held up to scientific scrutiny:
- Acetaldehyde. As your liver breaks down alcohol it produces acetaldehyde, a short-lived but toxic by-product that contributes to inflammation in the liver, brain and gut.
- Inflammation. Alcohol triggers an immune response, releasing inflammatory signals that produce the classic flu-like fog: poor concentration, low mood and general misery.
- Dehydration. Alcohol is a diuretic, so you lose more fluid than you take in. Dehydration contributes to headache and thirst — though research suggests it's only one piece of the puzzle, not the whole story.
- Disrupted sleep. Alcohol fragments the second half of your night and suppresses REM sleep, so you wake less rested even after a full eight hours in bed.
- Congeners. Darker drinks like bourbon, brandy and red wine contain more congeners — chemical by-products of fermentation linked to more severe hangovers than clear drinks like vodka and gin.
Why some hangovers are worse than others
The biggest factor is simply how much you drank — more alcohol means a more severe and usually longer hangover. But several other things tilt the scales:
| Factor | Why it matters |
|---|---|
| Total alcohol | The dominant factor — severity tracks how many standard drinks you had, regardless of drink type or order |
| Age | Your liver slows, your body holds less water and your sleep quality drops, so recovery takes longer after 30 |
| Drinking on an empty stomach | Alcohol absorbs faster, pushing BAC higher for the same number of drinks |
| Congener-heavy drinks | Dark spirits and red wine are linked to longer, more painful hangovers |
| Poor sleep | A short or broken night compounds the fatigue and fog |
One myth worth killing: the order of your drinks makes no difference. "Beer before wine, feel fine" has been tested and debunked — total alcohol is what counts.
What actually helps (and what doesn't)
Australia's healthdirect is blunt about it: time is the only way to remove alcohol from your body, so there's no cure for a hangover. What you can do is ease the symptoms while you wait:
- Drink water to address dehydration — steadily, rather than litres at once.
- Eat simple food when your stomach allows it, to help stabilise blood sugar.
- Rest. If you can go back to bed, sleep is one of the most effective things you can give your body.
- Take pain relief if needed for a headache — following the packet directions.
As for the folklore — greasy breakfasts, coffee, "hair of the dog", hangover pills — the evidence is thin to non-existent. Australia's Therapeutic Goods Administration warns that no listed medicine can legitimately claim to cure a hangover. Hair of the dog deserves a special mention: more alcohol may briefly mask symptoms, but it delays recovery and prolongs the pain. Coffee can even make things worse, since caffeine is also a diuretic.
The only reliable prevention
Unsatisfying but true: the only guaranteed way to avoid a hangover is to drink less, or not at all. Australia's NHMRC guidelines recommend healthy adults have no more than 10 standard drinks a week and no more than 4 on any one day to reduce the risk of harm — and staying inside those limits also happens to keep most hangovers mild.
If you do drink, the practical levers are the ones that lower your total intake and slow absorption: eat before and while drinking, alternate alcoholic drinks with water, choose lighter-coloured drinks if you're congener-sensitive, and keep count of your standard drinks rather than guessing. A "few beers" can easily be six or seven standard drinks once stubbies, pints and pours are counted properly.
Frequently asked questions
How long does a hangover last?
Up to 24 hours for most people, sometimes longer after a heavy session. Symptoms usually peak when your BAC returns to around zero — typically the morning after — and then ease through the day.
Why do hangovers get worse as you get older?
Your liver processes alcohol more slowly with age, your body holds less water, and your sleep quality declines. The same night out costs more at 40 than it did at 22.
Does "hair of the dog" cure a hangover?
No. It may briefly mask symptoms, but it adds more alcohol for your body to clear, delaying recovery and prolonging the hangover.
Do darker drinks cause worse hangovers?
They can. Bourbon, brandy and red wine carry more congeners than vodka or gin, and congeners are linked to more severe hangovers. Total alcohol still matters far more than colour.
Can you speed up a hangover?
Not meaningfully. Your body clears alcohol at a fixed rate. Water, food, rest and pain relief ease symptoms, but only time ends a hangover.