Chronic diarrhoea means loose or watery stools, usually three or more times a day, lasting four weeks or longer. It has many possible causes. Most are treatable once the cause is found, so it is worth looking into rather than putting up with it.
Common causes
- Irritable bowel syndrome with diarrhoea
- Lactose intolerance, which is common in Asian adults, and sugar substitutes such as sorbitol in sugar-free products
- Medicines, such as metformin, magnesium supplements, some antacids and acid-reducing medicines, and antibiotics
- Infections that persist, such as some parasites
- Inflammatory bowel disease (Crohn’s disease and ulcerative colitis)
- Microscopic colitis, which is more common in older women. The bowel looks normal at colonoscopy, and inflammation is only seen on biopsies.
- Bile acid diarrhoea, which may follow gallbladder removal or occur on its own
- Small intestinal bacterial overgrowth (SIBO), coeliac disease, an overactive thyroid, and reduced enzymes from the pancreas, which can cause pale, oily stools that are hard to flush
- Bowel polyps or colorectal cancer, especially in older adults
Warning signs that need prompt assessment
- Blood in the stool
- Unintended weight loss
- Diarrhoea that wakes you at night
- Anaemia or low iron (see iron deficiency anaemia)
- Fever, or a family history of colorectal cancer or inflammatory bowel disease
Tests
- A careful history, including diet, alcohol, medicines and supplements, travel, and any previous surgery
- Blood tests, such as blood count, inflammation markers, thyroid function and a coeliac test
- Stool tests for infection and for bowel inflammation (calprotectin)
- A colonoscopy with biopsies, which are taken even if the bowel looks normal, to check for microscopic colitis
- Sometimes a gastroscopy with biopsies of the small bowel, breath tests, or scans
Treatment
Treatment depends on the cause, for example stopping a medicine that is responsible, adjusting the diet, treating an infection, or treating inflammation. While the cause is being found, it helps to:
- Drink enough fluids, and use oral rehydration solution if the diarrhoea is heavy
- Keep a short diary of food, medicines and symptoms
- Use anti-diarrhoea medicine only when advised, especially if there is blood or fever
Seek urgent care at an emergency department for diarrhoea with heavy bleeding, high fever, severe abdominal pain, or signs of dehydration such as dizziness, confusion or passing very little urine.
General information only. Reviewed by Dr Chia Chung King, 2026-11-07. Book a consultation.