Functional Diarrhea

The exact cause is not known. Food may move too quickly through the bowel, the gut may be unusually sensitive, or the gut bacteria and bile acids (digestive substances made by the liver) may play a role. Infection can sometimes trigger it. Stress and anxiety often worsen symptoms. Because many other conditions cause chronic diarrhoea, including coeliac disease, inflammatory bowel disease, microscopic colitis, bile acid diarrhoea, lactose intolerance and thyroid disease, these need to be excluded.

Chronic diarrhoea is common in the general population, and a good share of people with it turn out to have a functional cause. It affects both men and women and any adult age.

If you fast during Ramadan, diarrhoea can lead to dehydration, so discuss with your doctor whether fasting is safe for you. Large, rich or sweet iftar meals and strong coffee or tea can trigger symptoms in some people.

Diagnosis starts with a careful history and examination. Blood tests check for anaemia, inflammation, thyroid problems and coeliac disease. A stool test for inflammation (calprotectin) helps separate bowel inflammation from functional disease, and stool tests may look for infection. A colonoscopy (a camera test of the large bowel) with small tissue samples may be done, particularly if you are older or have warning signs, to look for conditions such as microscopic colitis. Tests for bile acid diarrhoea may be considered. Functional diarrhoea is diagnosed when these are normal and symptoms fit the pattern.

Daily habits can reduce how often symptoms flare.

• Keep a diary of foods, stress and bowel movements to find your triggers

• Eat regular meals and avoid very large meals

• Be active; regular gentle exercise helps the gut

• Learn stress-management techniques such as relaxation or mindfulness; talk to your doctor about gut-focused psychological therapy

• Drink enough fluid to replace losses

Diet is often the first step. Try changes one at a time and avoid restrictive diets without guidance.

• Reduce caffeine (coffee, tea, energy drinks), which speeds the bowel

• Limit sugar-free sweeteners such as sorbitol and xylitol found in sugar-free sweets and gum

• Cut back on very fatty or fried foods and large amounts of alcohol

• Soluble fibre (oats, psyllium) can firm the stool; avoid a sudden large increase in fibre

• Test for lactose or other food intolerance only with your doctor or dietitian's guidance

Medicines can help, but should be chosen with your doctor, as they are not suitable for everyone.

• Loperamide (an anti-diarrhoea medicine) can reduce frequency and urgency; your doctor advises how to use it safely

• Bile acid binders may help if bile acid diarrhoea is suspected

• Other medicines that calm the gut may be tried in persistent cases

• Do not use antibiotics or herbal laxatives on your own; review any regular medicines that can cause diarrhoea with your doctor

Procedures are used to look for other causes rather than to treat functional diarrhoea.

• Colonoscopy with biopsies helps exclude inflammation and microscopic colitis

• Upper endoscopy with small bowel biopsies checks for coeliac disease when blood tests suggest it

• Breath tests or other tests may be used in selected cases for bacterial overgrowth or sugar intolerance

Functional diarrhoea is not dangerous and does not lead to cancer or inflammatory bowel disease. Symptoms can be long-lasting and may fluctuate, but most people find a combination of diet changes, medicines and stress management brings good control.

• Which tests have excluded other causes of my diarrhoea?

• Could I have bile acid diarrhoea, coeliac disease or microscopic colitis?

• Is it safe for me to use loperamide, and how often?

• Would a dietitian or gut-focused psychological therapy help me?

This guide comes from the Saudi Gastroenterology Association (SGA) patient library, prepared by the Approved for publication by SGA; individual clinician review is ongoing. Last reviewed: 2026-04-24. It is for education and does not replace your doctor's advice.