Why Does Caffeine Give Me The Runs? Unpacking the Digestive Impact

October 22, 2025 •

4 min read

According to one study, up to 29% of participants reported an urge to have a bowel movement within 20 minutes of drinking coffee. For those who experience this, the question isn't 'if' but 'why', leading to a common search for answers to 'why does caffeine give me the runs?'. It turns out that your daily brew is a potent cocktail of stimulants, acids, and hormones that can all conspire to get your digestive system moving.

Quick Summary

Caffeine stimulates the colon's muscle contractions and triggers digestive hormone release, speeding up gut motility. Other compounds in coffee also play a role, making its effect stronger than other caffeinated drinks. Individual sensitivity and additions like dairy are also significant factors in this common laxative reaction.

Key Points

Caffeine is a stimulant: It acts on the nervous system and also stimulates the muscles of the colon, increasing muscle contractions (peristalsis) that move waste through the digestive tract.
Hormones are triggered: Coffee prompts the release of hormones like gastrin and cholecystokinin (CCK), which signal the body to increase colon activity and speed up digestion.
Not just caffeine: Other compounds in coffee, such as chlorogenic acids, also contribute by increasing stomach acid and speeding up the digestive process, which is why decaf coffee can have a milder laxative effect.
Individual sensitivity varies: People with sensitive digestive systems, like those with IBS or lactose intolerance, are more likely to experience diarrhea from coffee, especially with added dairy.
Timing matters: The effect is often strongest in the morning due to the natural gastrocolic reflex, which is more active after waking and is stimulated by drinking.
Management is possible: Reducing intake, switching to decaf, drinking with food, and opting for dairy alternatives can all help minimize coffee-induced digestive upset.

The Stimulant Effect on Gut Motility

Caffeine is a well-known central nervous system stimulant, but its stimulating effects extend to the entire body, including the digestive tract. Your colon is lined with smooth muscle that contracts in a wave-like motion called peristalsis, pushing waste through the digestive system. Caffeine activates and increases these contractions, essentially putting your bowel movements on fast-forward. When this process is accelerated, the stool has less time to solidify as water is reabsorbed, resulting in looser, watery stools and the sudden urgency to go.

Hormones That Speed Things Up

Beyond its direct effect on muscle contractions, coffee consumption triggers the release of several hormones that significantly influence digestive function.

Gastrin: This hormone signals the stomach to produce and release gastric acid, which helps break down food. More importantly, it stimulates colonic motility, speeding up the entire process.
Cholecystokinin (CCK): Released after eating and drinking, this hormone can also stimulate colon activity and contribute to the laxative effect.

The Role of Other Coffee Compounds

Interestingly, studies have shown that decaffeinated coffee can also stimulate bowel movements, although its effect is milder than regular coffee. This indicates that caffeine isn't the sole culprit. Several other compounds naturally present in coffee contribute to its unique digestive impact.

Chlorogenic Acids: These antioxidants increase stomach acid levels, which speeds up the movement of food through the digestive tract.
N-alkanoyl-5-hydroxytryptamides: These unique compounds stimulate stomach acid and bile production, further promoting a quickened digestive process.
Melanoidins: Formed during the roasting process, these compounds have a prebiotic effect that feeds beneficial gut bacteria, indirectly promoting regularity.

Why Only Coffee, and Not Other Caffeinated Drinks?

For many, coffee has a much more pronounced effect than other caffeinated beverages like tea or energy drinks. While the caffeine content is a contributing factor, the complex interaction of coffee's other compounds with the body's natural reflexes makes it unique.

The Gastrocolic Reflex

The gastrocolic reflex is a natural bodily reaction where the stomach signals the colon to contract to make room for incoming food and drink. Coffee, especially a warm cup first thing in the morning when the colon is most active, appears to be a particularly effective trigger of this reflex.

Impact on Gut Motility: Regular Coffee vs. Other Drinks


Factor	Regular Caffeinated Coffee	Decaffeinated Coffee	Water
Effect on Colon Motility	Stimulates colon activity significantly, 60% more than water.	Stimulates colon activity mildly, 23% more than water.	Has minimal impact, mostly related to hydration.
Hormone Release	Triggers robust release of gastrin and CCK.	Causes a milder but still present release of gastrin.	Does not trigger significant hormonal release.
Unique Compounds	Contains the full spectrum of coffee acids and compounds.	Still contains chlorogenic acids and other compounds.	Lacks coffee-specific compounds.

When the Runs Are More Than Just an Inconvenience

For some individuals, coffee's digestive effects can be a source of significant discomfort rather than just a morning ritual. People with pre-existing gastrointestinal issues are often more susceptible.

Irritable Bowel Syndrome (IBS): Caffeine can exacerbate symptoms for individuals with IBS, especially the diarrhea-predominant type. The stimulating effect on the colon can trigger cramping, bloating, and more urgent bowel movements.
Lactose Intolerance: Many people add dairy products like milk or cream to their coffee. For those who are lactose intolerant, this can be a major contributor to gas, bloating, and diarrhea, often incorrectly blamed on the coffee itself.

How to Manage Coffee-Induced Diarrhea

If you find yourself routinely running to the bathroom after your coffee, there are several adjustments you can make to mitigate the effect without giving up your morning ritual entirely.

Reduce your intake: Lowering the amount of coffee you drink daily or in a single sitting can reduce the stimulating effect on your gut. Many find that moderation is key.
Switch to decaf: Although decaf can still cause some stimulation, the effect is significantly less intense for many individuals.
Try alternative additives: If you suspect dairy is the issue, switch to a plant-based milk alternative like oat or almond milk.
Pair with a meal: Drinking coffee on an empty stomach can intensify its effect. Having it with a meal, particularly one high in fiber, can buffer the acids and slow down digestion.
Consider alternative hot beverages: Warm liquids can trigger the gastrocolic reflex, so switching to a soothing herbal tea might provide a gentler morning nudge for your system.
Stay hydrated: Counteract the potential diuretic effect of caffeine by drinking plenty of water throughout the day, especially if you're experiencing loose stools.

Conclusion

For many, the link between caffeine and loose stools is a familiar, if slightly inconvenient, reality. The effect is a culmination of caffeine's stimulating properties, coffee's unique chemical compounds, and the body's natural hormonal and reflex responses. While the reaction can be bothersome, it is not inherently harmful for most healthy individuals and may even aid in regularity. By understanding the mechanisms at play and making simple adjustments to your consumption habits, you can better manage coffee's digestive impact and continue to enjoy your daily cup. If symptoms are severe or persistent, it's always best to consult with a healthcare provider to rule out underlying digestive conditions.

For more information on digestive health and diet, you can refer to the articles available on the Harvard Health website.

Frequently Asked Questions

Yes, it is a very common effect. The caffeine and other compounds in coffee act as stimulants on the digestive tract, increasing colon contractions and speeding up bowel movements, which can result in loose stools or diarrhea.

Yes, though the effect is typically milder than with regular coffee. Other compounds in coffee, like chlorogenic acids, still trigger digestive processes, so decaf can also stimulate bowel movements.

Coffee contains a unique mix of compounds, including acids and melanoidins, that work alongside caffeine to stimulate the digestive system more effectively. Other caffeinated drinks don't have this same cocktail of compounds.

This is due to the gastrocolic reflex, a natural reaction where the stomach signals the colon to contract when food or drink enters. Since the colon is already more active in the morning, coffee can trigger this reflex almost immediately.

Yes, if you have lactose intolerance, the dairy added to your coffee can contribute to digestive issues like gas, bloating, and diarrhea. Consider switching to a lactose-free or plant-based alternative.

While it can help with occasional constipation for some, relying solely on coffee is not ideal. A balanced diet with fiber, adequate hydration, and regular exercise is crucial for healthy bowel function. Over-reliance might mask an underlying issue.

If your symptoms are severe, persistent, or accompanied by other discomfort, it is best to reduce your caffeine intake and consult a healthcare professional. It could indicate a heightened sensitivity or an underlying digestive condition like IBS.