Indigestion can cause diarrhea, and the two symptoms frequently occur together. Between 11% and 27% of people with chronic indigestion (functional dyspepsia) also meet the criteria for irritable bowel syndrome, which commonly includes diarrhea. Whether from a stomach bug, a food sensitivity, or a medication side effect, the same trigger often irritates both the upper and lower digestive tract at once.
How Upper GI Distress Leads to Diarrhea
Your stomach and colon are in constant communication. When food enters the stomach and stretches its walls, stretch receptors trigger what’s called the gastrocolic reflex, a coordinated signal through the nervous system woven into your gut wall. This reflex ramps up movement in the colon to make room for incoming food. It’s the reason many people feel the urge to have a bowel movement shortly after eating.
When the stomach is already irritated or inflamed, this reflex can fire more aggressively than normal. The colon responds with stronger, more frequent contractions known as mass movements, which push contents through faster than the body can absorb water from them. The result is loose or watery stools. In severe cases, an exaggerated gastrocolic reflex contributes to dumping syndrome, where food moves through the digestive tract so rapidly it causes both malnutrition and persistent diarrhea.
Common Causes of Both Symptoms
Viral Gastroenteritis
The classic stomach bug, often caused by norovirus or rotavirus, infects the intestinal lining and produces both upper and lower GI symptoms simultaneously. Watery diarrhea, abdominal cramping, nausea, and vomiting typically appear together and resolve within one to three days. This is one of the most straightforward explanations when indigestion and diarrhea hit at the same time, especially if they come on suddenly.
Poorly Absorbed Carbohydrates
Certain sugars that the small intestine absorbs poorly can cause bloating, cramping, and stomach discomfort in the upper gut while simultaneously pulling water into the lower intestine and triggering diarrhea. These are collectively called FODMAPs, and they’re found in a wide range of everyday foods: dairy products, wheat-based breads and cereals, beans and lentils, onions, garlic, and fruits like apples, pears, cherries, and peaches. If your symptoms flare predictably after meals, a specific food group may be the culprit. A low-FODMAP elimination diet, where you temporarily remove these foods and reintroduce them one at a time, is one of the most effective ways to identify your triggers.
Small Intestinal Bacterial Overgrowth
When bacteria that normally live in the large intestine proliferate in the small intestine, they start fermenting food before your body has a chance to absorb it properly. This bacterial overgrowth produces gas and bloating (which feels like indigestion) while also breaking down bile salts that your body needs to digest fats. Without those bile salts, fat passes through undigested, causing diarrhea. The bacteria also damage the intestinal lining, further reducing absorption of carbohydrates and proteins. Over time, this leads to unintentional weight loss and nutritional deficiencies alongside the daily discomfort of nausea, bloating, fullness after eating, and loose stools.
Medications
Several common medications cause both indigestion and diarrhea as side effects. Metformin, widely prescribed for type 2 diabetes, triggers GI symptoms in roughly one out of three people who take it, with diarrhea and nausea being the most frequent complaints. NSAIDs like ibuprofen and naproxen can irritate the stomach lining while also disrupting the lower gut. Antibiotics, particularly amoxicillin-clavulanate, alter gut bacteria in ways that produce both upper stomach discomfort and diarrhea. SSRIs, a common class of antidepressants, sometimes cause nausea and diarrhea when first started, though this typically fades within a few weeks.
Functional Dyspepsia and IBS Overlap
Some people have chronic indigestion with no identifiable structural cause (functional dyspepsia) alongside irritable bowel syndrome. Research puts the overlap at roughly 11% to 27% of patients, depending on the population studied. The prevailing explanation is that both conditions share a root problem: heightened sensitivity in the gut’s nervous system and disordered motility throughout the digestive tract. If you’ve had recurring indigestion and diarrhea for months without an obvious dietary or medication trigger, this overlap is worth exploring with a gastroenterologist.
What Helps Both Symptoms
Bismuth subsalicylate, the active ingredient in Pepto-Bismol, is one of the few over-the-counter options specifically indicated for both indigestion and diarrhea. It works by coating the digestive lining and reducing inflammation in the stomach and intestines. For short-term flare-ups from food triggers or mild stomach bugs, it can address both ends of the problem at once.
Beyond that, the most effective approach depends on what’s driving the symptoms. If specific foods are the trigger, an elimination diet narrows down the offenders. If a medication is the likely cause, the timing of symptoms relative to when you started the drug is the biggest clue. For bacterial overgrowth, treatment targets the excess bacteria directly, and symptoms often improve within days of starting the right course of therapy.
Eating smaller, more frequent meals can reduce the intensity of the gastrocolic reflex, which helps when large meals seem to set off both discomfort and urgency. Cutting back on fatty foods also eases the workload on a gut that’s already struggling to digest and absorb properly.
Signs That Need Prompt Attention
Most episodes of combined indigestion and diarrhea resolve on their own or with minor adjustments. But certain patterns warrant faster evaluation: blood in your stool, difficulty swallowing, persistent vomiting, or unintentional weight loss. Diarrhea lasting more than a few days, especially with abdominal pain, can signal something beyond a simple stomach bug. If indigestion comes with chest heaviness, jaw or arm pain, shortness of breath, or sweating, those are cardiac warning signs that require emergency care, not digestive remedies.