Understanding Functional Diarrhea

Functional diarrhea is a health condition in which a person experiences chronic diarrhea without any clear-cut cause. It is one of the functional gastrointestinal disorders (FGD), which are defined as recurrent digestive system problems without any accompanying signs of a disease, injury, or structural problem identified on diagnostic testing.

A lack of abnormalities on diagnostic tests does not mean that functional diarrhea and FGD are not valid, real, or important. The symptoms are real and can cause negative health effects, and you may benefit from lifestyle modifications or medical treatment.

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The Rome IV diagnostic criteria categorize FGD, including functional diarrhea, according to specific definitions.

Functional diarrhea criteria are:

  • The experience of loose or watery stools
  • Lack of pain with the diarrhea
  • Diarrhea occurring in at least 75% of bowel movements
  • At least six months of symptoms, at least three months of which must be consecutive
  • No identifiable cause (structural or biochemical)

Functional Diarrhea and Irritable Bowel Syndrome

Irritable bowel syndrome (IBS) is a type of FGD. When chronic diarrhea is the predominant symptom of IBS, diarrhea-predominant irritable bowel syndrome (IBS-D) may be diagnosed.

Functional diarrhea is characterized by a lack of abdominal pain, while IBS-D can cause abdominal pain. Both disorders involve frequent loose stools and may also involve such symptoms as urgency, gas, bloating, mucus in the stool, and feelings of incomplete evacuation.

Functional diarrhea is often considered a subtype of IBS-D.


Functional diarrhea is diagnosed through a process of exclusion. This means that you can be diagnosed with functional diarrhea only after other digestive disorders or health problems have been ruled out.

Typically, your healthcare provider will take your health history, do a physical examination, and may order diagnostic lab tests, such as blood work and a stool sample analysis.

Other possible tests can include imaging examinations, such as abdominal computed tomography (CT), ultrasound, or magnetic resonance imaging (MRI). Invasive tests such as a colonoscopy or an endoscopy can also help identify a causative medical condition.

Differential Diagnoses

Possible causes of diarrhea that need to be ruled out before a diagnosis of functional diarrhea is made include:

  • Gastrointestinal (GI) infection, including chronic infection. Infections notoriously cause loose stools. Most GI infections last no longer than a few weeks and typically resolve on their own. But chronic infections, which can be diagnosed with a stool sample, may cause prolonged symptoms.
  • Medication side effects. A number of medications can cause diarrhea, and you may develop this side effect even if you have taken medication for a while without diarrhea.
  • Diet. Various food allergies and sensitivities can cause loose stools without pain. You may notice a pattern of diarrhea occurring after you eat certain foods.
  • Celiac disease. This can develop with age and may be associated with gluten sensitivity, or may cause diarrhea regardless of your diet.
  • Gluten sensitivity. This is becoming a more common problem. You can try a gluten-free diet for a few weeks to see if there is a decrease in your diarrhea.
  • Lactose intolerance. A relatively common problem, lactose intolerance is characterized by diarrhea and cramping after eating or drinking dairy products.
  • Fructose malabsorption. It can be more difficult to identify than lactose intolerance, but cutting out foods that contain fructose for a few weeks can help you assess whether fructose contributes to your diarrhea.
  • Malabsorption due to bariatric surgery. Malabsorption is a common problem caused by bariatric surgery, in which parts of the GI system are removed to prevent over-eating and excessive absorption of calories.
  • Gastrointestinal cancer. Cancer may cause bleeding and weight loss, and may manifest with a variety of less-common symptoms, such as diarrhea.
  • Autonomic neuropathy. Often caused by chronic alcohol use, neuropathy can impair the function of nerves throughout the body, including the nerves of the GI system, potentially causing diarrhea.

You may also be at higher risk of developing functional diarrhea after having your gallbladder removed.


Typically, treatment of functional diarrhea is aimed at reducing symptoms through dietary modifications, such as eliminating possible trigger foods and slowly increasing fiber intake. If stress appears to be a possible contributing factor, stress-management strategies might be helpful.

Your healthcare provider may give you a prescription or recommendation for one of the following medications to reduce your diarrhea:

6 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. Schmulson MJ, Drossman DA. What is new in Rome IV. J Neurogastroenterol Motil. 2017;23(2):151-163. doi:10.5056/jnm16214

  3. Saha L. Irritable bowel syndrome: Pathogenesis, diagnosis, treatment, and evidence-based medicine. World J Gastroenterol. 2014;20(22):6759-73. doi:10.3748/wjg.v20.i22.6759

  4. Bul V, Sleesman B, Boulay B. Celiac disease presenting as profound diarrhea and weight loss - a celiac crisis. Am J Case Rep. 2016;17:559-61. doi:10.12659/AJCR.898004

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Additional Reading

By Barbara Bolen, PhD
Barbara Bolen, PhD, is a licensed clinical psychologist and health coach. She has written multiple books focused on living with irritable bowel syndrome.