Key takeaway: In one survey, 29% of healthy young adults said coffee gave them the urge to go. Gut-pressure studies found coffee can wake up the colon within about four minutes in those people, with an effect similar in size to a big meal. Decaf did it too, so caffeine isn't the whole story.
You pour the first cup, take a few sips, and about ten minutes later your morning plans include a short, urgent detour. If that sounds familiar, you're in good company, and scientists have been curious about it for decades.
So what's actually going on? Is it the caffeine, the heat, the acidity, or something else hiding in the cup? Here's what the research measured.
Does coffee make everyone poop?
No. It's common, but it's not universal.
In a classic study from Sheffield, England, researchers surveyed 99 healthy volunteers aged 17 to 27 about their bathroom habits. 29% said coffee gave them a desire to go (Brown, Cann & Read, Gut 1990). That means most people in the survey did not report it.
The researchers then put that self-reported effect to the test. They measured pressure activity in the lower colon (the rectosigmoid area) of 14 volunteers after a cup of black, unsweetened coffee. Here's what they saw:
| Group | What happened after coffee |
|---|---|
| 8 people who said coffee made them go | Motor activity rose within about 4 minutes and lasted at least 30 minutes |
| 6 people who said it didn't | No increase in activity |
| Everyone, after plain hot water | No increase in activity |
So the "coffee urge" isn't in your head. For people who feel it, the colon really does respond, and fast.
How fast does coffee make you poop?
In that 1990 study, the lower colon responded within about four minutes of drinking coffee in people who reported the urge (Brown et al., 1990). That's quick. Too quick, in fact, for the coffee to have traveled anywhere near the colon, which is a clue that the signal starts higher up, likely in the stomach, and gets relayed down the line.
A separate trial found coffee didn't speed up how fast a liquid meal left the stomach or moved through the small intestine (Boekema et al., Eur J Clin Invest 2000). In other words, coffee isn't pushing things through the whole system faster. Its best-documented effect is on the colon itself.
Is coffee as strong as a meal?
Pretty much, according to one study. Researchers at the University of Iowa placed pressure sensors along the colons of 12 healthy adults and gave them four things on the same day, in random order: black coffee (150 mg caffeine), decaf, warm water and a 1,000-calorie meal (Rao et al., Eur J Gastroenterol Hepatol 1998).
| Drink or meal | Colon activity, per the study |
|---|---|
| 1,000-calorie meal | Strong response |
| Caffeinated coffee | Similar to the meal, 60% stronger than water, 23% stronger than decaf |
| Decaf coffee | In between: not significantly different from water or regular coffee, and lower than the meal |
| Warm water | Weakest response |
The authors' conclusion: caffeinated coffee stimulates colonic motor activity, with a magnitude similar to a meal. Not bad for a drink with almost no calories.
Is it the caffeine?
Partly, maybe. But not entirely. Several clues point to other compounds in coffee:
- Decaf worked too. In the 1990 study, both regular and decaf coffee raised lower-colon activity in responders (Brown et al., 1990).
- It's not just the warm liquid. Hot water did nothing in that study, and a review concluded coffee's gut effects can't be explained by its volume, acidity or osmolality, adding that caffeine can't fully account for them (Boekema et al., Scand J Gastroenterol 1999).
- Lab muscle tests agree. In a 2022 study in rats, both regular coffee and decaf made strips of intestinal and colon muscle contract in the lab, and the researchers found that compounds other than caffeine triggered those contractions (Hegde et al., Nutrients 2022). Animal tissue isn't a person, but it fits the human data.
So caffeine may add a little extra push, but researchers have not pinned down a single "poop molecule." Coffee contains a very long list of bioactive compounds, and reviews say much about how they act on the gut is still unknown (Iriondo-DeHond et al., Nutrients 2021).
What is the gastrocolic reflex, and does coffee trigger it?
The gastrocolic reflex is your gut's built-in "make room" signal: when food reaches the stomach, the colon tends to get more active. That's one reason a big breakfast can send you to the bathroom.
Coffee seems to tap into the same messaging system. Studies found it nudges the release of gut hormones that normally rise with a meal:
- Gastrin. In 10 healthy volunteers, both regular and decaf coffee caused a prompt, lasting rise in the hormone gastrin. Average totals were about 2.3 times (regular) and 1.7 times (decaf) the control drink (Acquaviva et al., J Clin Gastroenterol 1986).
- Cholecystokinin (CCK). In a small study of regular coffee drinkers, both regular and decaf raised CCK and made the gallbladder contract, about 33% after regular and 29% after decaf (Douglas et al., Am J Clin Nutr 1990).
Researchers haven't proven that these hormones are the whole reason coffee gets you moving. But the timing (minutes, not hours), the meal-like size of the response, and the fact that decaf shares it all fit the idea that coffee "talks" to the colon from the stomach. A 2022 review of the research listed stimulation of colon motility among coffee's fairly clear effects on the digestive tract (Nehlig, Nutrients 2022).
Does decaf make you poop?
It can. In the studies above, decaf raised lower-colon activity in people who were sensitive to coffee (Brown et al., 1990), raised gastrin (Acquaviva et al., 1986) and triggered gallbladder contractions (Douglas et al., 1990). In the Iowa trial, though, regular coffee had a bigger effect than decaf (Rao et al., 1998). So expect decaf to do a gentler version of the same thing, if you're someone who feels it at all.
Why does coffee hit some people and not others?
The honest answer: nobody knows for sure. The studies above found big differences between "responders" and "non-responders," and they mostly tested small groups of healthy young adults. Your body, your routine and what you ate (or didn't) all likely play a part. If you're curious about other ways coffee interacts with your gut, see our deeper look at coffee, the gut and the brain.
A few practical notes:
- Morning matters. Many people drink their first cup soon after waking, when the gut is often already gearing up for the day. For more on timing, read the best time to drink coffee.
- Coffee still counts as fluid. Moderate coffee doesn't dehydrate you, according to the research we covered in does coffee dehydrate you.
- Mind the total. If you're stacking cups, see how long caffeine lasts.
If coffee regularly upsets your stomach, or you notice a lasting change in your bathroom habits, that's worth a conversation with your doctor. People with digestive conditions such as IBS or IBD should ask their healthcare provider how coffee fits for them.
A cup worth the trip
If your morning cup is going to get your whole system up and running, it should be a cup you trust. That's why I started Edge in St. Paul in 2020. Pure Health Coffee is a Peruvian single-origin Arabica, medium roasted for notes of chocolate, caramel and roasted nuts. Every lot is tested by Eurofins, and our posted sample reports showed no detectable mycotoxins, including ochratoxin A below 1 ppb. See them on our lab results page, and learn what we test for on our mold-free coffee page. Results apply to the samples tested.
Want to dial in your brew? Try our coffee to water ratio cheat sheet. Shipping is free on every order, always.
FAQ
Why does coffee make you poop? Studies found coffee can stimulate the colon within minutes, with an effect similar in size to a meal. It also raises gut hormones such as gastrin and CCK, and compounds other than caffeine appear to be involved.
Does coffee make everyone poop? No. In a 1990 survey of 99 healthy young adults, 29% said coffee gave them an urge to go. In gut-pressure tests, only those who reported the urge showed increased colon activity.
How long after drinking coffee do you have to poop? In people sensitive to it, one study measured increased lower-colon activity within about four minutes of drinking coffee, lasting at least 30 minutes.
Does decaf coffee make you poop? It can. Decaf raised lower-colon activity in sensitive people and raised the hormone gastrin, though one trial found regular coffee had a stronger effect on the colon than decaf.
Is it the caffeine that makes you poop? Not entirely. Decaf produced similar effects in several studies, and a 2022 lab study found compounds other than caffeine made gut muscle contract. Caffeine may add to the effect.
Is it the heat or acidity of coffee? Probably not. Hot water caused no colon response in a 1990 study, and a review concluded coffee's gut effects can't be explained by its volume, acidity or osmolality.
This article is general information about coffee and caffeine research, not medical advice. Results from individual studies apply to the people and conditions they tested. If you're pregnant, take medication or have a health condition, ask your healthcare provider about coffee and caffeine.
Sources
- Brown SR, Cann PA, Read NW. Effect of coffee on distal colon function. Gut. 1990;31(4):450-453. https://pubmed.ncbi.nlm.nih.gov/2338272/
- Rao SS, Welcher K, Zimmerman B, Stumbo P. Is coffee a colonic stimulant? Eur J Gastroenterol Hepatol. 1998;10(2):113-118. https://pubmed.ncbi.nlm.nih.gov/9581985/
- Boekema PJ, Samsom M, van Berge Henegouwen GP, Smout AJ. Coffee and gastrointestinal function: facts and fiction. A review. Scand J Gastroenterol Suppl. 1999;230:35-39. https://pubmed.ncbi.nlm.nih.gov/10499460/
- Boekema PJ, Lo B, Samsom M, Akkermans LM, Smout AJ. The effect of coffee on gastric emptying and oro-caecal transit time. Eur J Clin Invest. 2000;30(2):129-134. https://pubmed.ncbi.nlm.nih.gov/10651837/
- Acquaviva F, DeFrancesco A, Andriulli A, et al. Effect of regular and decaffeinated coffee on serum gastrin levels. J Clin Gastroenterol. 1986;8(2):150-153. https://pubmed.ncbi.nlm.nih.gov/3745848/
- Douglas BR, Jansen JB, Tham RT, Lamers CB. Coffee stimulation of cholecystokinin release and gallbladder contraction in humans. Am J Clin Nutr. 1990;52(3):553-556. https://pubmed.ncbi.nlm.nih.gov/2393014/
- Hegde S, Shi DW, Johnson JC, et al. Mechanistic study of coffee effects on gut microbiota and motility in rats. Nutrients. 2022;14(22):4877. https://pubmed.ncbi.nlm.nih.gov/36432563/
- Iriondo-DeHond A, Uranga JA, Del Castillo MD, Abalo R. Effects of coffee and its components on the gastrointestinal tract and the brain-gut axis. Nutrients. 2021;13(1):88. https://pubmed.ncbi.nlm.nih.gov/33383958/
- Nehlig A. Effects of coffee on the gastro-intestinal tract: a narrative review and literature update. Nutrients. 2022;14(2):399. https://pubmed.ncbi.nlm.nih.gov/35057580/
- Edge Coffee sample Eurofins report AR-24-JF-015481-01 (Pure Health Coffee green beans, Mar 2024), via /pages/lab-results