Why Alcohol Gives You Diarrhea, and Why It's Worse the Next Morning

It's the morning after. The first coffee has barely gone down and you're already heading for the bathroom, fast. Maybe it happened last night too, somewhere between the third pint and the taxi home. Loose, urgent stools after drinking are common enough to have earned a nickname, "beer poops", and the reasons behind them are fairly well understood. Here is what alcohol does on its way through your gut, why the next morning tends to be the worst of it, and when it's a reason to see a doctor.

Alcohol hurries everything along

Your small intestine moves food with two kinds of muscle action. One pushes food forward. The other holds it in place long enough for it to be digested and for water to be absorbed. Alcohol weakens the holding movements, so what you ate and drank moves through faster than it should. In people who drink heavily over time, that shorter transit time is one of the reasons diarrhea is so common.

Alcohol also gets in the way of absorption itself. In animal studies, a single dose of alcohol blocks the uptake of water and sodium from the small intestine. In people who drink regularly, healthy or not, water and sodium absorption is markedly reduced. Water that stays in your gut has only one way out, and it arrives as loose, watery stool.

It irritates the lining of your gut

Alcohol irritates the lining of the stomach directly and makes it release more acid, which is part of why a heavy night leaves you queasy. The irritation reaches further down too. Even in healthy people, a single episode of heavy drinking can cause erosions and bleeding in the duodenum, the first stretch of the small intestine.

Over time, heavy drinking also seems to make the gut more sensitive to sugar. People who drink heavily often react more to foods high in sugar, such as sweets and sweetened juices. Sugary mixers may be doing you no favours.

Why beer nights can hit hardest

Plenty of people notice it most after beer. Research comparing drinks head to head is thin, so nobody can say for certain why, but a few things set beer apart.

• Drinks with a low alcohol content, such as beer and wine, strongly increase stomach acid. Strong drinks above about 15 percent tend to slow the stomach down, and beer is far below that.
• A few pints is a lot of fizzy liquid. The NHS advice for people with irritable bowel syndrome (IBS) is to avoid drinking lots of alcohol or fizzy drinks.
• Most beer is brewed from barley, which contains gluten. Coeliac disease is a reaction to gluten, and diarrhea and bloating are among its main symptoms. If beer reliably sets you off while wine and spirits don't, and bread or pasta bother you too, ask a doctor about it.

Some guts are also more sensitive than others. In a study where women kept a daily diary for about a month, those with IBS had more diarrhea the day after drinking four or more drinks. Women without IBS showed no clear link between their drinking and their gut symptoms.

Why the morning after is the worst part

Your colon is quiet while you sleep. In a classic study that recorded colon activity around the clock, movement was minimal during sleep and rose sharply at waking and after meals. Most of the strong, sweeping contractions that push stool toward the exit happened soon after people woke up, and they were often felt as an urge to go.

Breakfast adds to it. Through the gastrocolic reflex, a stomach stretched by food signals the colon to start moving, often within minutes of eating. Coffee can do the same. In one study, close to a third of people said coffee made them need the toilet, and in those people it stepped up activity in the lower colon within four minutes, with or without caffeine.

So on a hangover morning, it all stacks up. Alcohol has already sped things along and left extra water in your gut. Then you wake up, eat and have a coffee, and your colon gets three separate signals to empty at once. Alcohol also makes you pee more, so between the toilet trips and the diarrhea you're losing a lot of fluid. Keep sipping water through the day.

The rest of a heavy night shows up the same morning, and our piece on what one night of drinking does to your body covers the bigger picture. For the swollen, gassy feeling that often comes with it, see alcohol bloating and the beer belly.

When to see a doctor

In general, the NHS says diarrhea usually stops within 5 to 7 days. Some signs mean you shouldn't wait it out. Based on NHS advice:

• Get an urgent appointment or call NHS 111 (or your own urgent care line) if your poo is black or dark red, or if you have bloody diarrhea. Very dark or black poo can mean bleeding in the stomach or gut. Iron tablets, liquorice and blueberries can also darken it.
• Get advice if diarrhea lasts more than 7 days, or if you show signs of dehydration such as dark pee or peeing much less than usual.
• See a doctor if you've had blood in your poo for 3 weeks, or your poo has been softer, thinner or longer than normal for 3 weeks.
• Call an ambulance or go to the emergency department if you're bleeding non-stop or there's a lot of blood, for example if the toilet water turns red or you see large clots.

Diarrhea after most drinking sessions, or stomach pain that keeps coming back, is worth raising with a doctor even without those signs. Heavy drinking is hard on the lining of the stomach and gut, and a doctor can check what's going on.

What changes when you drink less

The gut effects follow the dose. In the diary study of women with IBS, binge days were the ones most clearly linked to next-day diarrhea, while light and moderate drinking was only weakly linked or not linked at all. The erosions and bleeding in the gut lining come with heavy episodes. In the stomach, abstinence can at least partly reverse the changes that years of heavy drinking cause.

There is little research on how quickly the bowel settles after people cut back, so your own pattern is the best guide. Jotting down how much you drank next to how the next morning went is a simple way to find the point where your gut starts to object. If you want a structured way to bring the number down, our cut back or quit plan walks through it.

If you drink heavily every day, stopping suddenly can be dangerous. Talk to a doctor first. The NHS lists anxiety, sweating, shaking, a racing heart and trouble sleeping among the signs of withdrawal. Seek urgent care for severe shaking you can't control, confusion, seeing or hearing things that aren't there, a seizure, or a racing heart with heavy sweating.