Recurring diarrhea that comes and goes, sometimes for weeks or months, usually points to a chronic digestive issue rather than a simple stomach bug. If your loose stools have persisted for more than four weeks total, even with gaps of normal bowel movements in between, something is driving the pattern. The most common culprits are food intolerances, irritable bowel syndrome, bile acid malabsorption, and medication side effects, though inflammatory conditions need to be ruled out too.
IBS Is the Most Common Explanation
Irritable bowel syndrome, particularly the diarrhea-predominant type, is the single most frequent diagnosis behind on-and-off loose stools. The hallmark is abdominal pain at least one day per week for three months or more, where the pain is tied to bowel movements or comes alongside changes in how often you go or what your stool looks like. Stress, certain meals, hormonal shifts, and disrupted sleep can all trigger flare-ups, which is why the pattern feels so unpredictable.
IBS does not cause visible damage to your intestines. If a doctor performed a colonoscopy, the lining would look completely normal. That’s frustrating when you want answers, but it also means IBS is not progressing toward something more dangerous. The gut-brain connection plays a central role: your intestines are more sensitive to normal signals, and your nervous system amplifies them into cramping and urgency.
Food Intolerances You Might Not Recognize
Lactose intolerance gets the most attention, but fructose malabsorption is surprisingly common and often overlooked. When your small intestine can’t fully absorb fructose, the unabsorbed sugar sits in the gut and draws water into the intestinal space through osmotic pressure. That fluid rush is what produces the watery stool, bloating, and gas that follow certain meals.
The tricky part is that fructose hides in foods you wouldn’t suspect. Apples, pears, and mangoes contain more free fructose per serving than most other fruits. Soft drinks sweetened with high-fructose corn syrup are another major source, averaging about 37% more fructose than glucose. If your diarrhea tends to flare after fruit, juice, soda, or honey, fructose malabsorption is worth investigating. A hydrogen breath test can confirm it, though an elimination diet where you remove high-fructose foods for two to three weeks is often the simplest starting point.
Bile Acid Malabsorption
Your liver produces bile acids to help digest fat. Normally, your small intestine reabsorbs most of them before they reach the colon. When that recycling system fails, excess bile acids flood the colon and trigger watery diarrhea, often urgently and unpredictably. This condition, bile acid malabsorption, is far more common than most people realize. Studies have found it in up to 50% of patients originally diagnosed with “functional” diarrhea, meaning diarrhea with no obvious cause.
Bile acid diarrhea tends to be worse after fatty meals and often strikes in the morning. It’s frequently misdiagnosed as IBS because the symptoms overlap so heavily. If you’ve been told you have IBS but haven’t responded to typical treatments, this is one of the first things worth exploring with your doctor.
Medications That Cause Ongoing Loose Stools
Several widely prescribed medications can produce intermittent diarrhea as a side effect, and the connection isn’t always obvious because symptoms may not start immediately. Metformin, one of the most common diabetes medications, is a well-known offender. Antibiotics disrupt gut bacteria and can trigger diarrhea that persists weeks after you finish the course. Proton pump inhibitors (used for acid reflux), magnesium supplements, and certain blood pressure medications also belong on this list. If your diarrhea started within a few months of beginning a new medication or increasing a dose, that timing matters.
Signs That Point to Something More Serious
Most on-and-off diarrhea turns out to be functional, meaning uncomfortable but not dangerous. However, certain symptoms suggest inflammation or structural disease that needs investigation. Blood or black color in your stool, unintentional weight loss, fevers, and anemia are all markers of inflammatory bowel disease (Crohn’s disease or ulcerative colitis) rather than IBS. IBD causes visible, destructive inflammation in the intestinal lining that shows up on imaging and biopsies. IBS does not.
Another condition that flies under the radar is microscopic colitis, where the colon looks normal during a colonoscopy but biopsies reveal inflammation at the cellular level. There are two forms: one involves a buildup of collagen protein in the colon wall, and the other shows an increase in certain white blood cells. The only way to catch it is through tissue samples taken during a scope, so if your doctor performs a colonoscopy, make sure biopsies are part of the plan even if the lining appears healthy.
Bacterial Shifts in the Small Intestine
You may have come across the term SIBO, or small intestinal bacterial overgrowth, as a possible explanation. The idea is that excess bacteria in the small intestine ferment food prematurely, producing gas, bloating, and diarrhea. Research from Mayo Clinic, however, has raised serious questions about how SIBO is diagnosed. The most commonly used breath tests have very low accuracy, with high rates of false positives. More recent research suggests that the real issue may not be too many bacteria, but rather a shift in the types of bacteria present in the small intestine. If a practitioner diagnoses you with SIBO based solely on a breath test, it’s worth seeking a second opinion before committing to treatment.
How to Start Narrowing It Down
Tracking your symptoms for two to three weeks gives you and your doctor the best starting material. Note what you ate, your stress level, the timing of loose stools, and any accompanying symptoms like cramping, urgency, or bloating. Patterns often emerge quickly. Diarrhea that worsens after dairy or fruit points toward an intolerance. Episodes tied to stressful days or poor sleep lean toward IBS. Morning urgency after fatty dinners suggests bile acid issues.
A stool calprotectin test is one of the most useful early steps your doctor can order. It measures a protein released by inflamed intestinal tissue. Normal levels strongly suggest that your intestines are not inflamed, effectively ruling out IBD and other inflammatory causes without needing invasive testing. High levels, on the other hand, signal that imaging or a colonoscopy should come next. Very high levels are closely linked to IBD or certain bacterial infections, while moderately elevated results can reflect celiac disease, infections, or even regular use of anti-inflammatory painkillers like ibuprofen.
Basic blood work checking for anemia, celiac antibodies, and thyroid function rounds out the initial workup. An overactive thyroid speeds up gut motility and can produce intermittent diarrhea that mimics IBS, and celiac disease is present in roughly 1 in 100 people, many of whom go years without a diagnosis.