Introduction

Chronic diarrhea in adults is more than just an upset stomach. When loose, watery stools last for four weeks or more, they can rob you of energy, cause weight loss, affect work and relationships, and sometimes indicate conditions that need treatment. This guide explains what chronic diarrhea is, common causes of chronic diarrhea, how doctors investigate it, real tests and treatments, and practical steps you can try at home all explained in plain language with insights from real world .

What is chronic diarrhea in adults?

Chronic diarrhea in adults means loose or watery stools (three or more times a day or more than your usual amount) that last for four weeks or more. It can be intermittent (comes and goes) or constant. Causes range from irritable bowel syndrome (IBS) and inflammatory bowel diseases (Crohn’s disease, ulcerative colitis) to infections (Giardia), medication side effects (antibiotics, metformin), malabsorption (celiac disease, pancreatic insufficiency), microscopic colitis, and diarrhea.

Doctors start with a careful history (time, stool type, weight loss, recent antibiotics, travel) and simple tests (blood tests, stool studies, fecal calprotectin) and move on to more targeted tests such as colonoscopy or breath tests as needed. Treatment depends on the cause from diet changes and loperamide to antibiotics (for certain infections or small intestinal bacterial overgrowth) to bile acid sequestrants, budesonide for microscopic colitis, or specific therapy for IBD to relieve symptoms. If diarrhea lasts longer than four weeks or you have red flags (fever, weight loss, blood in the stool), see a doctor.

What is chronic diarrhea in adults? (Definition and types)

Clear definition

Chronic diarrhea in adults is defined as loose or watery stools that persist for four weeks or longer (sometimes defined as ≥3 loose stools per day for at least 4 weeks). Short term (2-4 weeks) may be considered persistent. Less than 2 weeks is usually severe. The four week cutoff helps doctors decide which tests may be useful.

Types by mechanism (how diarrhea occurs)

Doctors often think of chronic diarrhea in three broad categories because treatment varies by mechanism:

Watery diarrhea caused by problems with osmotic (poorly absorbed solutes), secretory (excessive intestinal secretions), or bile acids.

Inflammatory diarrhea caused by inflammation of the intestines (ulcerative colitis, Crohn’s, infections) and often contains blood or mucus and fever.

Steatorrhea heavy, oily, foul smelling stools caused by poor absorption of fat (pancreatic insufficiency, small bowel disease).

Understanding the pattern helps your doctor choose the right tests and treatments.

Why Chronic Diarrhea Occurs: Common Causes of Chronic Diarrhea

(We will use short, clear explanations and everyday analogies.)

Irritable Bowel Syndrome with Diarrhea (IBS-D)

IBS-D is a very common cause of chronic diarrhea and abdominal pain. Think of the gut as a piano: In IBS, the keys are overly sensitive and sometimes play too fast causing pain and loose stools. Estimates of the prevalence of IBS worldwide vary. Several large studies have put the prevalence at around 9-15%, depending on the criteria and region. Doctors may diagnose IBS and treat it symptomatically when there are no “danger signs.”

Read in Details About: Irritable Bowel Syndrome

Inflammatory bowel disease (IBD) – Crohn’s disease, ulcerative colitis

IBD causes actual inflammation in the lining of the gut. If your intestine is inflamed, it’s like a rough, irritated surface that can’t absorb water normally  hence the persistent diarrhea, often with blood, weight loss, and fever. IBD requires specialist care and specific anti-inflammatory or immunosuppressive treatments.

Post infectious causes (after an episode of gastroenteritis)

Sometimes a stomach bug triggers long term changes in the gut  a kind of “aftershock.” Post infectious IBS can occur after food poisoning or traveler’s diarrhea. Estimates suggest that a significant minority (about 5-12% in some studies) develop chronic intestinal symptoms after an infection.

Bile acid diarrhea (bile acid malabsorption)

Bile acids normally help digest fats. If they reach the large intestine, they act like a detergent and draw water into the intestines, causing watery diarrhea. This condition is under-recognized but may explain symptoms such as chronic watery diarrhea, or IBS-D, in 1 in 4 to 3 people. It responds to bile acid binders such as cholestyramine.

Microscopic colitis

Microscopic colitis is inflammation that can be seen under a microscope (colonoscopy may appear normal). It is common in older adults (especially women) and causes chronic watery diarrhea. Treatment is often budesonide, which has good short term responses but can recur after stopping treatment.

Malabsorption and pancreatic insufficiency

If your pancreas does not release the enzymes needed to digest fats (chronic pancreatitis, cystic fibrosis in adults, previous pancreatic surgery), stools may be oily and greasy. Pancreatic enzyme replacement often helps.

Celiac disease

An immune response to gluten can damage the small intestine and cause chronic diarrhea, weight loss, and malnutrition. A simple blood test (tTG IgA) and confirmation by a gastroenterologist can identify this treatable cause.

Read in Detail About: Gluten Free Foods

Medications and Toxins

Many common medications cause diarrhea: antibiotics (which can also trigger C. difficile), metformin, magnesium supplements, some heart medications, and proton pump inhibitors or NSAIDs (associated with microscopic colitis). Always review recent medication changes with your doctor.

Read In Detail About: Diarrhea After Antibiotics ?

Chronic Infections and Parasites

Giardia and other parasitic infections can persist (especially if left untreated) and cause chronic diarrhea. A history of travel, camping, or contaminated water are clues. The CDC provides clear guidance on diagnosis and treatment.

Causes of  Chronic Diarrhea in Adults

When to worry: Red flags for chronic diarrhea in adults

If diarrhea lasts more than 4 weeks, especially with any of the following, seek immediate medical attention:

• Unintentional weight loss
• Persistent fever
• Blood or black stools (visible hematemesis or melena)
• Severe abdominal pain or signs of obstruction
• Nocturnal diarrhea that wakes you up
• New symptoms after age 50 or a family history of colon cancer or inflammatory bowel disease
• Signs of malnutrition (hair loss, easy bruising, numbness)

These “red flags” raise the possibility of inflammatory bowel disease, infection, or malignancy and usually trigger urgent tests such as a colonoscopy. For guidance on when to see a doctor, see the Mayo Clinic patient pages.

Diagnosis: How doctors diagnose chronic diarrhea in adults.

Diagnosis is stepwise: Start with a history and basic tests, then escalate as needed.

1. What your doctor will ask (history)

• Onset and duration: When did it start? Is it continuous or intermittent?
• Stool description: Watery, greasy, bloody? Urgent? Nighttime symptoms?
• Triggers: New foods, recent antibiotics, travel, pets, sexual exposure.
• Medications: Recent increases (metformin, laxatives, PPIs).
• Weight loss, fever, extraintestinal symptoms (rash, joint pain).

A careful history often leads the way.

2. First line tests (simple and widely available)

• CBC (complete blood count) – looks for anemia (bleeding) or infection.
• Basic chemistry, check electrolytes and kidney function (dehydration).
• Thyroid test (thyrotoxicosis can cause diarrhea).
• Celiac serology (TTG IgA).
• Stool tests – routine culture if infection is suspected, ova and parasites (if travel risk), C. difficile testing when relevant.
• Fecal calprotectin or lactoferrin, non invasive markers of intestinal inflammation; helpful in distinguishing IBD (inflammatory) from IBS (functional). Fecal calprotectin shows good sensitivity and specificity for identifying organic bowel disease.

3. Targeted and specialized tests

Colonoscopy with biopsy  necessary to diagnose alarm features or microscopic colitis (biopsy may be normal looking but abnormal under the microscope).

SeHCAT (where available)  Nuclear medicine test for bile acid malabsorption; not universally available but shows bile acid diarrhea in a significant proportion of patients with chronic watery diarrhea.

Hydrogen breath test  for lactose intolerance or small intestinal bacterial overgrowth (SIBO).

Stool elastase  for exocrine pancreatic insufficiency.

Imaging (CT/MRI)  when structural disease is suspected.

4. Practical Diagnostic Tip

If initial tests (blood, stool, calprotectin) suggest no inflammation and symptoms are not consistent with IBS-D, extensive invasive testing can often be avoided but red flags or treatment failure should prompt referral and further evaluation. AAFP guidance outlines a practical step-by-step approach.

Treatment of Chronic Diarrhea in Adults

Treatment of chronic diarrhea is specific to the cause. Below are common strategies organized by possible diagnosis.

Symptom Control Measures (Useful When Working on a Diagnosis)

• Rehydration and Electrolyte Replacement  Especially When Stools Are Frequent
• Loperamide (Imodium)  A safe, over-the-counter option in many cases to control watery stools (use with caution if fever or bloody diarrhea is present).

Avoid simple sugars and caffeine once symptoms resolve.

If IBS-D is suspected.

• Dietary interventions  A low-FODMAP diet often reduces symptoms. Work with a dietitian for a trial and gradual reintroduction.

• Loperamide for immediate symptom control.

• Rifaximin a non-absorbed antibiotic that has been shown to help IBS-D symptoms in randomized trials (significant improvement in bloating, stool consistency, and global symptoms after a 2-week course). Re-courses may help select patients.

• Bile acid sequestrants (cholestyramine, colesevelam) if bile acid diarrhea is suspected.

• Neuromodulators (low-dose tricyclics or SSRIs) may help with pain and bowel sensitivity in some patients under expert guidance.

• Psychological approaches, CBT or gut directed hypnotherapy may help because gut-brain interactions play a role in IBS.

If inflammatory bowel disease (IBD)

IBD requires gastrointestinal care for inflammation and immune therapy (aminosalicylates, immunomodulators, biologics). Do not use loperamide in severely active IBD without expert advice.

Microscopic colitis

Budesonide is the best-studied therapy for inducing remission. Symptoms often improve rapidly, but relapse after cessation is common and may require a maintenance strategy.

Bile acid diarrhea

Bile acid sequestrants  (cholestyramine or colesevelam) bind bile acids and often greatly reduce watery stools. If no other causes are found, consider a trial of investigational or experimental treatments.

Pancreatic insufficiency

Pancreatic enzyme replacement (oral pancreatic enzymes with food) significantly improves fatty stools and weight gain in pancreatic insufficiency.

Chronic and recurrent C. difficile infection

Giardiasis  Treatable with metronidazole, tinidazole, or nitazoxanide; consult CDC guidance for complicated cases.

C. difficile  Targeted testing and treatment are needed. Recurrent infections sometimes require advanced treatments (fedaxomycin, fecal microbiota transplant). CDC pages summarize diagnosis and treatment.

Diet, lifestyle, and home care for chronic diarrhea in adults

Small changes often add up, here’s a clinician’s practical toolbox.

Diet Basics (What to Try, What to Avoid)

• If IBS-D is suspected, try a low FODMAP approach for 2-6 weeks.
• Avoid excessive caffeine, sugar alcohols (sorbitol, xylitol), and large amounts of fruit juice.
• Low fat diets may help with steatorrhea until the cause is treated.
• Introduce soluble fiber (psyllium) gradually, it can thicken stools in watery diarrhea for some people. Be cautious if bloating worsens.
• If diarrhea follows antibiotics, consider probiotics (certain strains may help) and test for C. difficile if symptoms are severe. See our internal link for post-antibiotic guidance: [Diarrhea After Antibiotics].

Lifestyle and Medication Review

• Keep a medication log: Many medications cause diarrhea metformin, magnesium, some antihypertensives, and antibiotics. Review with your doctor.
• Avoid unnecessary NSAIDs if microscopic colitis is suspected.
• Manage stress: Stress management often reduces the frequency and urgency when IBS is present.

Doctor’s Perspective: Rarely Discussed Medical Insights

These are the things I see in the clinic that don’t make headlines but change patients’ lives.

• Bile acid diarrhea is often missed: Many patients labeled “IBS-D” actually have bile acid malabsorption  a simple trial of bile acid binders or the SeHCAT test (where available) can make a difference. Clinicians should think about the causes of bile acid, especially after cholecystectomy or in those who don’t respond to standard IBS treatments.
• Microscopic colitis hides behind a routine colonoscopy: Because the colon looks normal on scope, a biopsy is important. Women over 50 with watery diarrhea often have microscopic colitis a diagnosis missed until biopsies are taken.
• A medication review is the quickest win: I routinely tell patients to stop taking unnecessary medications (magnesium supplements, some herbal laxatives, or newer antidiabetics) under supervision. Symptoms often improve within days.
• Persistent, low grade parasite infection: Giardia can linger for months in people who have never been tested or have received incomplete treatment especially after camping or traveling. CDC guidance helps with diagnosis and second-line treatment.
• Treat the person, not just the stool: Chronic diarrhea impairs quality of life social withdrawal, work limitations, and anxiety are common. Combining psychosocial care, input from a dietitian, and social support improves outcomes more than medication alone.

A real world case (telling a short story to make it relevant)

Sarah, 48, teacher “I had been having watery stools for 6 months and felt exhausted. I was told it was stress. I lost 6kg and had to stop working.”

Her history showed no watery diarrhoea, urgency, or blood. She had a normal colonoscopy but biopsies showed microscopic colitis. A short course of budesonide reduced symptoms within two weeks. A careful medication review stopped the NSAID she was taking daily. With diet tweaks and follow up, she returned to work and gained back her weight.

Takeaway: A normal looking colonoscopy does not rule out treatable causes a biopsy and careful medication review may be key.

Putting It Together: A Practical Checklist for Patients

If you have chronic diarrhea in adults, bring this checklist to your doctor:

• Timeline: When did it start? How many bowel movements per day? Any weight loss?
• Stool diary: Watery vs. fatty vs. bloody; What foods preceded symptoms
• Medication list: Include over-the-counter, supplements.
• Red flags: Fever, blood, weight loss, nighttime symptoms write them down.
• Previous tests/treatments: Stool tests, colonoscopy, antibiotics used.
• Impact: Note how symptoms affect work, sleep, mood.
• Bringing organized information speeds diagnosis and reduces retesting. The AAFP and specialty guidelines support a step-by-step approach that starts with simple tests and progresses as needed.

Practical Approach (Short and Actionable)

• Don’t ignore diarrhea that lasts more than four weeks. Chronic diarrhea in adults deserves a diagnosis.
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• Start with a careful history and simple tests (blood, stool tests, fecal calprotectin).
• A drug review often looks for reversible causes.
• If common treatments fail, consider bile acid diarrhea and microscopic colitis—they respond to specific treatments.
• Red flags = a fast track to the doctor. Bleeding, weight loss, fever, or severe pain warrant immediate action.

References:

Centers for Disease Control and Prevention – Guidance on Parasitic Infections (Giardia) and C. difficile.

Mayo Clinic – A patient-friendly overview of diarrhea, tests, and when to see a doctor.

Selected PubMed Studies: Bile Acid Diarrhea, Fecal Calprotectin Efficacy, Rifaximin Trials, Budesonide Evidence (cited inline above).

Conclusion: You are not alone; many causes are treatable

Chronic diarrhea in adults can be frightening and exhausting, but a careful, step-by-step approach a thorough history, focused tests, medication review, and targeted treatment often leads to a resolution or plan that restores quality of life. Start with your primary care physician, bring a clear timeline and list of medications, and ask about fecal calprotectin, bile acid causes, and microscopic colitis if initial care does not help. Early diagnosis and simple treatments (diet, bile acid binders, antibiotics for certain conditions, or budesonide for microscopic colitis) often work.

Call to Action (CTA)

If this article was helpful, please comment below with your experiences or questions  I read them and will answer them. If you are a patient with persistent symptoms, make an appointment with your doctor and bring the checklist above. 

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🧑‍⚕️ About the Author

Dr. Asif, MBBS, MHPE

Dr. Asif is a licensed medical doctor and qualified medical educationist with a Master’s in Health Professions Education (MHPE) and 18 years of clinical experience. He specializes in gut health and mental wellness. Through his blogs, Dr. Asif shares evidence-based insights to empower readers with practical, trustworthy health information for a better, healthier life.

⚠️ Medical Disclaimer

This blog is intended for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or another qualified healthcare provider with any questions you may have regarding a medical condition. Never disregard or delay medical advice based on content you read here.