Why does alcohol upset my stomach?
Queasiness, heartburn, a churning gut and the dreaded next-day runs — a sensitive stomach is one of the most common complaints after a night out. The reason is simple: alcohol irritates your digestive system from your throat all the way to your bowel.
Your gut meets alcohol long before it reaches your bloodstream or your head, so it's no surprise drinking can leave your stomach feeling rough. The good news is that most of what alcohol does to your digestion is well understood — and once you know the mechanisms, it's easier to head off the worst of it. Here's what's going on down there.
Alcohol stirs up acid and irritates the lining
Alcohol is an irritant. When it hits your stomach it prompts the lining to produce more acid than usual while also inflaming and wearing at that protective lining. That combination drives the uncomfortable, burning, queasy feeling that can come on even while you're still drinking.
Stronger drinks do more damage. High-concentration spirits — anything around 40% ABV and up — can directly irritate the tissue they touch on the way down. A neat whisky or a round of shots is harder on your stomach than the same amount of alcohol spread across weaker, more diluted drinks.
It slows your stomach down — and that makes you queasy
You'd think alcohol would speed everything up, but in the stomach it does the opposite. Drinking delays gastric emptying — it increases the time food and fluid sit in your stomach before moving on. That sluggishness, on top of the irritation and the toxic by-products your liver is scrambling to process, is a major reason heavy drinking brings on nausea and vomiting.
Vomiting is partly your body trying to expel a poison it can't keep up with — unpleasant, but the real danger is when someone has drunk so much they can't protect themselves.
Heartburn: the valve to your throat loosens
Between your stomach and your oesophagus (the tube to your throat) sits a ring of muscle that normally stays shut to keep stomach contents where they belong. Alcohol relaxes that valve — the lower oesophageal sphincter. Once it loosens, the acidic contents of your stomach can rise back up, which you feel as heartburn or acid reflux: a burning behind the breastbone, sometimes a sour taste at the back of the throat.
Because alcohol also raises how much acid your stomach is making, there's more of it to come back up — and when a night ends lying down to sleep, gravity stops helping, making the small hours a classic time for reflux. Both one-off big nights and regular drinking can trigger it.
Why alcohol gives you diarrhoea
The upset doesn't stop at your stomach. Further down, alcohol speeds up the muscle contractions that push contents through your large intestine, and it interferes with how much water your gut reabsorbs. Normally your large intestine soaks water back out of your waste to firm it up. When alcohol rushes everything through faster and leaves more water behind, the result is loose, watery stools — often the morning after.
A few things make it worse: sugary mixers and sweet drinks pull extra water into the bowel, the caffeine in some pre-mixes is itself a gut stimulant, and a big session means a lot of fluid. For most people the runs settle within a day as the alcohol clears and the gut recovers.
The whole gut, at a glance
| What you feel | What alcohol is doing | Worst with… |
|---|---|---|
| Queasiness, burning | More stomach acid + irritated lining | Strong spirits, empty stomach |
| Nausea & vomiting | Slowed stomach emptying + toxic overload | Heavy, fast sessions |
| Heartburn / reflux | Relaxed valve to the throat + more acid | Lying down after drinking |
| Diarrhoea | Faster bowel transit + less water reabsorbed | Sugary & caffeinated drinks |
| Bloating, indigestion | Irritation and inflammation (gastritis) | Big or regular drinking |
When irritation becomes gastritis
If the stomach lining gets inflamed enough, it has a name: gastritis. Alcohol can bring it on acutely — from a single heavy session — or chronically, building up over months and years of regular drinking. It can feel like a gnawing or burning pain high in the stomach, indigestion, feeling uncomfortably full after eating, or nausea and vomiting.
A one-off bout usually settles as the lining recovers, but repeated irritation never gets the chance to heal. Over the long term, ongoing gastritis raises the risk of stomach ulcers and other problems, and heavy drinking is linked to cancers of the digestive system including the mouth, oesophagus and bowel. Chronic heavy drinking also damages the gut's ability to absorb nutrients — particularly proteins, vitamins and minerals.
How to settle your stomach — and prevent it next time
You can't stop alcohol being an irritant, but you can give your gut a lot less to deal with:
- Don't drink on an empty stomach. Food slows how fast alcohol is absorbed and puts a buffer between the alcohol and your stomach lining. Eating before and while you drink is one of the most effective things you can do — see our guide on drinking on an empty stomach.
- Pace yourself. Around one standard drink an hour gives your stomach and liver time to keep up, rather than overwhelming them.
- Alternate with water. It dilutes the alcohol hitting your stomach and helps with the dehydration that piles onto the next-day misery.
- Go easier on the irritants. Strong neat spirits, sugary mixers, and fizzy drinks are all harder on the gut. Longer, weaker, less sweet drinks are gentler.
- Know your numbers. Australia's guidelines recommend no more than 10 standard drinks a week and no more than 4 on any one day for healthy adults. Treat that as a ceiling, not a target.
If your stomach is already upset, the honest answer is that time does most of the work. Sip water or an electrolyte drink, stick to bland food when you can face it, and go easy on painkillers — some, like aspirin and ibuprofen, can irritate an already inflamed stomach, so check the label. For everyday tactics, the government's healthdirect tips for safe drinking and Victoria's Better Health Channel guide to how alcohol affects your body are good starting points. The UK's Drinkaware rundown on alcohol and your stomach and the Cleveland Clinic's overview of gastritis go deeper into the biology.
Frequently asked questions
Why does alcohol upset my stomach?
Alcohol irritates your digestive system from top to bottom. It prompts your stomach to make more acid and inflames the lining, which causes that queasy, burning feeling. It also slows how quickly your stomach empties, relaxes the valve between your stomach and throat so acid can rise up as heartburn, and speeds things up in the bowel, which is why many people get diarrhoea. Stronger drinks and bigger sessions irritate the gut more.
Why does alcohol give me diarrhoea the next day?
Alcohol speeds up the muscle contractions that move contents through your large intestine and interferes with how much water your gut reabsorbs. Food passes through faster and arrives in the bowel still watery, so you get loose stools. Sugary mixers, sweet drinks and caffeine in some pre-mixes make it worse. It usually settles within a day.
Why does drinking give me heartburn or acid reflux?
Alcohol relaxes the ring of muscle at the bottom of your oesophagus — the valve that keeps stomach contents down. When it loosens, acid can rise into your throat and chest, which you feel as heartburn. Alcohol also increases stomach acid, so there's more to come back up, and lying down after drinking makes it easier for acid to travel the wrong way.
Can one big night cause gastritis?
Yes. Gastritis — inflammation of the stomach lining — can be brought on acutely by a single heavy session, or build up chronically over years of regular drinking. It can feel like a gnawing or burning pain high in the stomach, indigestion, feeling overly full, or nausea. A one-off bout usually settles, but repeated irritation raises the risk of ulcers, so persistent symptoms are worth seeing a doctor about.
How do I stop alcohol upsetting my stomach?
Drink less. If you do drink, don't drink on an empty stomach, pace yourself at around one standard drink an hour, alternate every drink with water, and go easier on strong spirits, sugary mixers and fizzy drinks. Staying within the Australian guidelines of no more than 10 standard drinks a week and 4 on any day keeps the strain on your stomach lower.