Why Do I Get Diarrhea From Alcohol?

Why alcohol causes diarrhea

There is no single mechanism but several that add up. It helps to separate them, because they do not weigh the same after one night as with regular drinking.1

• Irritation of the lining. A single episode of heavy drinking can cause erosions in the duodenum and injury to the upper small bowel.1
• Poorer absorption of water and salt. The gut fails to recover part of the fluid it receives, and that fluid ends up in the stool. As you will see, this is mainly an effect of sustained drinking.2
• A leakier gut barrier. In heavy drinkers, the lining lets through more molecules than it should.6
• Changes in gut bacteria. Alcohol alters the microbiota and is associated with small intestinal bacterial overgrowth.57
• What comes with the drinking. Large, fatty meals, sugary mixers, gas, caffeine and little sleep. All of these speed up the gut too.

Next-day diarrhea: what the evidence says

Here is a surprising fact. When it was measured directly in healthy volunteers, putting alcohol into the small bowel on a single occasion did not change water and sodium absorption.2 Nor did it impair nutrient absorption.3 In other words, one night's alcohol does not "flush" the gut on its own.

So why do so many people get diarrhea the next day? Mainly because of the amount and how sensitive your gut is. The best study on this followed women with and without irritable bowel syndrome for a month using daily diaries. In those with irritable bowel syndrome, having four or more drinks in a day was clearly linked to diarrhea, nausea, stomach pain and indigestion the next day. Light or moderate drinking was barely associated with symptoms. And in women without irritable bowel syndrome, no drinking pattern was linked to symptoms.4

The practical conclusion: if next-day diarrhea happens to you often, the problem is probably not just the alcohol but a particularly sensitive gut. It is very typical of diarrhea-predominant irritable bowel syndrome, which I discuss in how I treat continuous diarrhea and gas and on the page on irritable bowel syndrome.

If you drink often: when diarrhea becomes regular

With sustained drinking the picture changes. In the same type of volunteer study, two weeks of alcohol on a folate-poor diet clearly reduced water and sodium absorption, to the point that the gut started secreting fluid. On an adequate diet the effect was smaller but still present.2 Poorer small-bowel absorption has also been documented in people with sustained heavy drinking.8

On top of that, alcohol makes several conditions more likely, and they show up as diarrhea:

• Bacterial overgrowth. In a breath-test study, 58% of moderate drinkers tested positive, against 38.9% of non-drinkers.7
• Microscopic colitis. In two large cohorts of US nurses, with more than 200,000 participants, drinking 5-15 g of alcohol a day almost doubled the risk, and 15 g or more multiplied it by 2.3.9 I explain it in microscopic colitis.
• Pancreas. Alcohol is one of the major causes of chronic pancreatitis, and when the pancreas stops making enzymes, fat is not digested.10 If you have been found to have low elastase, read low fecal elastase.

The full picture of what alcohol does to the digestive tract, from the esophagus to the liver, is in alcohol's effects on the digestive system.

Which drinks cause the most diarrhea?

There are no good studies comparing drinks head to head, so caution is wise. What we do know:

• Amount and speed matter more than type. Binge drinking causes the most symptoms the next day.4
• Wine and beer are among the items people with irritable bowel syndrome most often blame: almost a third link them to their symptoms.11
• Mixed drinks add sugar, gas and sometimes caffeine, which on their own can speed up transit and cause gas.
• Drinking on an empty stomach makes alcohol reach the gut sooner and more concentrated.

If certain drinks clearly affect you more, it makes sense to cut back on them. To see which foods might be behind your symptoms, read food intolerances.

What to do

If you already have diarrhea

• Rehydrate with water and, if the diarrhea is heavy, with an oral rehydration solution.
• Eat light for a day or two and don't drink again until your gut has settled.
• If you take other medicines, check before taking an antidiarrheal on your own.

To stop it happening again

• Avoid binge drinking. Spreading fewer drinks over time causes far fewer symptoms.4
• Drink slowly, with food, alternating with water.
• Notice whether a particular drink affects you more.
• If you have a sensitive gut, alcohol is usually one of the factors most worth cutting down.

Five myths about alcohol and diarrhea

How I assess it in clinic

The first step is to separate two very different situations: occasional diarrhea after heavy drinking, which usually points to a sensitive gut, and diarrhea that has become regular. In the second case I do a structured work-up: blood tests including celiac serology, fecal calprotectin and, depending on the history, a breath test, fecal elastase or colonoscopy with biopsies. It is the same approach I describe on the page on chronic diarrhea.

And I always talk openly about alcohol use. Not to judge, but because cutting down is usually the single measure that improves symptoms most, and because catching liver or pancreatic damage early changes the outlook.

Related reading

Alcohol's effects on the digestive system Microscopic colitis How I treat continuous diarrhea and gas

When diarrhea becomes chronic, a colonoscopy with biopsies can reveal causes that cannot be seen with the naked eye.

Frequently asked questions

References

1. Bode C, et al. Effect of alcohol consumption on the gut. Best Pract Res Clin Gastroenterol. 2003;17(4):575-92. PubMed (opens in a new tab)
2. Mekhjian HS, et al. Acute and chronic effects of ethanol on fluid transport in the human small intestine. Gastroenterology. 1977;72(6):1280-6. PubMed (opens in a new tab)
3. Pfeiffer A, et al. Effect of ethanol on absorption of a nutrient solution in the upper human intestine. Scand J Gastroenterol. 1993;28(6):515-21. PubMed (opens in a new tab)
4. Reding KW, et al. Relationship between patterns of alcohol consumption and gastrointestinal symptoms among patients with irritable bowel syndrome. Am J Gastroenterol. 2013;108(2):270-6. PubMed (opens in a new tab)
5. Engen PA, et al. The Gastrointestinal Microbiome: Alcohol Effects on the Composition of Intestinal Microbiota. Alcohol Res. 2015;37(2):223-36. PubMed (opens in a new tab)
6. Keshavarzian A, et al. Leaky gut in alcoholic cirrhosis: a possible mechanism for alcohol-induced liver damage. Am J Gastroenterol. 1999;94(1):200-7. PubMed (opens in a new tab)
7. Gabbard SL, et al. The impact of alcohol consumption and cholecystectomy on small intestinal bacterial overgrowth. Dig Dis Sci. 2014;59(3):638-44. PubMed (opens in a new tab)
8. Krasner N, et al. Alcohol and absorption from the small intestine. 1. Impairment of absorption from the small intestine in alcoholics. Gut. 1976;17(4):245-8. PubMed (opens in a new tab)
9. Niccum B, et al. Alcohol Consumption is Associated With An Increased Risk of Microscopic Colitis: Results From 2 Prospective US Cohort Studies. Inflamm Bowel Dis. 2022;28(8):1151-1159. PubMed (opens in a new tab)
10. Struyvenberg MR, et al. Practical guide to exocrine pancreatic insufficiency - Breaking the myths. BMC Med. 2017;15(1):29. PubMed (opens in a new tab)
11. Böhn L, et al. Self-reported food-related gastrointestinal symptoms in IBS are common and associated with more severe symptoms and reduced quality of life. Am J Gastroenterol. 2013;108(5):634-41. PubMed (opens in a new tab)
12. Singh P, et al. Chronic, Noninfectious Diarrhea: A Review. JAMA. 2026;335(14):1250-1262. PubMed (opens in a new tab)