Most diarrhea is a short-lived bug that clears up in a few days. When loose or watery stools keep going for four weeks or more, doctors call it chronic diarrhea. It almost always has a cause that can be found, and most of those causes are treatable.
Common causes
- Irritable bowel syndrome (IBS-D): cramping tied to bowel movements, often worse with stress or certain foods. Read more about IBS and bloating.
- Food triggers: lactose; sugar alcohols such as sorbitol and xylitol in sugar-free gum, candy and protein bars; large amounts of fruit sugar, caffeine or alcohol.
- Medicines and supplements: metformin, magnesium, some antibiotics, and GLP-1 medicines such as Ozempic, Wegovy, Mounjaro and Zepbound. Don't stop a prescribed medicine on your own; ask the doctor who prescribed it.
- Bile acid diarrhea: common after gallbladder removal, often urgent, watery stools soon after meals.
- Microscopic colitis: watery diarrhea, most often in people over 50. The colon looks normal during a colonoscopy, so the diagnosis needs biopsies. Some common medicines, including NSAIDs and certain acid reducers, are linked to it.
- Celiac disease: a reaction to gluten that a simple blood test can screen for.
- Infections: Giardia, or C. diff after a course of antibiotics or a hospital stay.
- Crohn's disease and ulcerative colitis: often with blood, belly pain, weight loss or symptoms at night. See Crohn's disease and ulcerative colitis.
- Less common: an overactive thyroid, or too little pancreatic enzyme, which causes greasy, floating, hard-to-flush stools.
See a doctor soon if you have:
- Blood in the stool, or black stools
- Diarrhea that wakes you up at night
- Weight loss you can't explain
- Fever, or diarrhea that started after antibiotics or a hospital stay
- Low iron or anemia on blood work
- New diarrhea that started at 45 or older
- A family history of colon cancer, celiac disease, Crohn's or ulcerative colitis
Go to the ER for signs of dehydration (very little urine, dizziness when you stand, confusion), bloody diarrhea with a fever, or severe belly pain.
What to track before your visit
- How long it's been going on, and how many stools a day
- What it looks like: watery, greasy or bloody
- Whether it wakes you at night
- Everything you take, including supplements, sweeteners and protein bars
- Recent travel, antibiotics or gallbladder surgery
- What you've already tried, and whether it helped
What a GI doctor usually checks first
- Blood work, often including a celiac test and a thyroid check
- Stool tests: calprotectin, which flags inflammation, and tests for infections such as Giardia (and C. diff if antibiotics are involved)
- Sometimes a test or trial treatment for bile acid diarrhea
- A colonoscopy with biopsies when there are warning signs, when new symptoms start at 45 or older, or when the first tests don't explain things
The first round of lab testing follows the American Gastroenterological Association's guideline for chronic diarrhea.
What's reasonable to try in the meantime
If you have none of the warning signs above:
- Drink plenty of fluids. An oral rehydration drink helps if stools are very watery.
- Stop sugar-free gum and candy, and try two weeks without regular dairy (lactose-free milk is fine).
- Ease off caffeine and alcohol.
- A daily soluble fiber such as psyllium can firm up loose stools.
- Loperamide (Imodium) is fine for occasional use, but not if you have blood in the stool or a fever.
The bottom line
Diarrhea that has lasted a month isn't something to just live with. Most causes are common, easy to test for and treatable.
— Brian Frank, MD
Questions? Call (813) 400-0543 or send a message.
Board-certified gastroenterologist (ABIM). Published November 4, 2026.
Source: Smalley W, et al. AGA Clinical Practice Guidelines on the Laboratory Evaluation of Functional Diarrhea and Diarrhea-Predominant Irritable Bowel Syndrome in Adults. Gastroenterology, 2019. This page is general information, not medical advice. For a medical emergency, call 911.