Chronic Diarrhea for a Month (or More): 7 Causes, Gastroenterologist Explains.

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Chronic diarrhea for a month can be due to infectious or non-infectious causes. The most common causes are food intolerances, irritable bowel syndrome, medications, and chronic infections. 

Causes include:

  • Irritable bowel syndrome.
  • Food intolerance.
  • Medications such as metformin, antibiotics, and laxatives abused.
  • Chronic infections such as clostridium difficile, chronic Giardiasis, and others. 
  • Inflammatory bowel diseases such as Crohn’s disease and ulcerative colitis.
  • Other causes include endocrinal diseases, intestinal malignancy, radiotherapy, …etc.

1. Irritable bowel syndrome.

Irritable bowel syndrome is a functional disease affecting your digestive system. The main feature of IBS is recurrent abdominal pain associated with bowel habit changes.

IBS has a subtype called (Diarrhea-predominant IBS) or IBS-D. Diarrhea-predominant IBS can present with chronic diarrhea for a month or more. 


Very common; about 10-15% of people worldwide are affected by IBS (reference). More importantly, You may have IBS and be unaware of it. 

Too many people who have IBS don’t know they have it. Only 40% who match the criteria of IBS have an official diagnosis (reference).


Unknown. Many theories attempted to explain the cause of IBS. Food and psychological stress are the most frequent associations of IBS

Other explanations of IBS include 

  • SIBO (overgrowth of bacteria inside your small intestine).
  • Increased colon sensitivity to stretch (usual amounts of gas can lead to abdominal pain.
  • Post-infectious (IBS can develop after an attack of gastroenteritis).
  • Inflammation of your colon.

Learn more about the causes of IBS.

Features of IBS (Symptoms):

  • Abdominal pain. With IBS, you’ll experience pain at least one day per week for several months).
  • IBS can be diarrhea-predominant (which can cause diarrhea for a month or more).
  • Other types of IBS also exist. They include IBS-constipation, IBS-Mixed diarrhea, and constipation, and the unclassified type. Learn more.
  • Distension and bloating.
  • The symptoms (including diarrhea) (flare-ups and remissions) come and go.
  • With IBS, there are no fever, no vomiting, and no blood in the stool.

What to do?

IBS is a common condition. That’s why it came first on the list of causes of chronic diarrhea for a month. 

But you can’t diagnose IBS by yourself. If your symptoms are suspicious of IBS, you need to arrange a visit to your doctor. 

MORE: symptoms of IBS and how doctors diagnose it.

2. Food intolerance.


Food intolerance is the inability of your digestive system to handle certain types of food.

For example, the deficiency of an enzyme called “Lactase” inside your intestine leads to (lactose intolerance).

Lactose intolerance is the most common type of food intolerance. People with lactose intolerance experience symptoms (including diarrhea) whenever they drink milk or dairy.

Other types of food intolerance include:

  • Fructose intolerance: fructose is a sugar present in most fruits and honey.
  • FODMAP intolerance (as with patients with IBS): They are a group of carbohydrates. They rapidly ferment and produce intolerance symptoms.
  • Amines (as histamine) intolerance
  • Sulfate intolerance.
  • Caffeine intolerance.
  • Gluten intolerance (celiac disease): gluten is a protein present in wheat, rye, and barley. People with celiac disease can present 

How to suspect (symptoms):

  • Often, symptoms start soon after you eat the offending food.
  • Abdominal pain or cramps.
  • Acute or chronic diarrhea (for a month or more). Diarrhea continues as long as you continue to eat the offending food.
  • Nausea and anorexia (loss of appetite).
  • Gas and bloating.

Learn More about food intolerance.

Food allergy is another form of food sensitivity. The differences between food intolerance and food allergy are in the below table.


What to do if you have a food intolerance?

Food intolerance and food allergy are hard to diagnose. Chronic or intermittent diarrhea for months or years has to be evaluated by your doctor. 

Your doctor may ask you to keep a food diary. Also, He may order some intolerance tests to diagnose such a condition.

Avoiding the offending foods will improve your diarrhea. For example, people with lactose intolerance dramatically improve after cutting dairy products from their diet. 

3. Medications.

Medications are another frequent factor contributing to diarrhea. More than 700 medications can cause diarrhea. 

You may be taking a diarrhea-inducing drug, and you don’t know.

Examples of medications that cause diarrhea for a month or more:

  • Metformin: a commonly-prescribed drug for Diabetes Mellitus. 
  • Antibiotics: a single course of antibiotics for a few days can lead to chronic diarrhea for a month or several months. Antibiotics can kill the beneficial bacteria inside your intestine (learn more).
  • Gastritis & Peptic ulcer medications (antacids and PPIs): such as Calcium or magnesium-containing antacids, Omeprazole (Prilosec®), Esomeprazole (Nexium®), and others. 
  • Antidepressants: drugs that are used for psychological diseases and conditions such as anxiety, depression, and Irritable bowel syndrome. For example; Citalopram (Celexa®), Escitalopram (Lexapro®), Paroxetine (Paxil®).
  • Non-steroidal anti-inflammatory drugs such as Ibuprofen (Advil®) and diclofenac.
  • Colchicine (Mitigare®); is a drug used in gout and familial Mediterranean fever. 
  • ACE inhibitors (an anti-hypertensive medication).
  • Chemotherapy (anti-cancer treatment).

4. Chronic gut infections.

Some infections (especially bacterial and protozoal species) can cause prolonged diarrhea. 

Chronic infectious diarrhea can last for a month or several months and years.

The most common causes of chronic infections diarrhea include:

The symptoms of chronic infectious diarrhea are often less severe than its acute form. 

Besides diarrhea, you may suffer from abdominal cramps, nausea and vomiting, fever, and weight loss. 

Some infections can cause malabsorption such as Giardiasis. Your doctor must perform lab tests to diagnose such conditions as stool analysis and culture. 

5. Inflammatory bowel disease.

This is relatively less common than the causes enlisted above. inflammatory bowel disease (IBD) is different from irritable bowel syndrome (IBS).

IBS is a functional disease without obvious inflammation in your colon. On the other hand, IBD causes True inflammation and ulceration of your gastrointestinal tract. 

IBD includes:

  • Crohn’s disease → inflammation and ulcers anywhere inside your gut (from the mouth to the anus).
  • Ulcerative colitis → inflammation and ulcers confined to your colon. 

Inflammatory bowel disease can be a cause of chronic diarrhea (for a month or more).

Features of IBD (symptoms):

  • Abdominal pain (often in the lower abdomen).
  • Diarrhea for a month or several months (sometimes, diarrhea alternates with constipation).
  • Mucus in the stool.
  • Blood in stool.
  • The urgency to poop.
  • Unexplained fever, weight loss.
  • Anorexia (loss of appetite).
  • The inflammation and ulceration can be severe to cause perforation or form a mass inside your abdomen. 

IBD is a more severe disease. Its cause is still unknown. The diagnosis usually requires a colonoscopy to reveal the lesions. Your doctor may also order some blood tests or take a biopsy to diagnose you with IBD.

You cannot diagnose IBD by yourself. suspect IBD particularly if you suffer from bloody diarrhea, weight loss, and fever for months. 

IBD is treated with 5-amino salicylic acid (5-ASA) and may require medications that suppress your immunity. 

6. Post-cholecystectomy diarrhea.

Post-cholecystectomy diarrhea is a very common condition after gallbladder removal surgery. 

Some studies estimate that up to 20% of patients suffer from diarrhea for several weeks to several years after cholecystectomy. 

Your gallbladder acts as a storage place for bile until the next meal. Diarrhea is usually caused by the inability of your intestine to handle excess bile after the removal of the gallbladder.

symptoms (how to suspect):

  • History of gallbladder removal in the past few months.
  • diarrhea started soon after the removal of your gallbladder.
  • Diarrhea usually stops after a couple of weeks or a month, but it rarely lasts for years.
  • It is more evident after eating fatty foods. 

Diarrhea often resolves on its own, but you can talk to your doctor to confirm the diagnosis and to discuss the treatment options.

Avoiding fatty foods, heavy meals, and caffeine improves the condition. Some patients may need anti-diarrheal medications such as loperamide. 

Learn More about post-cholecystectomy diarrhea. 

7. Other (less common) causes of diarrhea for a month.

There are several causes of chronic diarrhea for months. You need to be evaluated by a doctor or gastroenterologist

  • Bile acid diarrhea: a condition caused by the inability of your intestine to handle bile, resulting in watery diarrhea with urgency. Learn More.
  • Celiac disease: an extreme form of food intolerance. extreme diarrhea, bloating and anemia result from ingestion of gluten. Gluten is a constituent of wheat, rye, and barley. Learn More. 
  • SIBO (small intestinal Bacterial Overgrowth): caused by abnormal replication of bacteria inside your small intestine. This results in chronic diarrhea, bloating, and malabsorption of nutrients. 
  •  Chronic pancreatitis: chronic inflammation in your pancreas (especially in alcoholics) can cause chronic diarrhea with abdominal pain in the upper part of your stomach. Learn More.
  • Diabetes Mellitus: Diabetes causes destruction to the nerves supplying your intestine and colon. A condition called “autonomic neuropathy” leads to chronic diarrhea for months or years. 
  • Hyperthyroidism (excess thyroid hormones).
  • Previous surgical resection of a part of your small intestine or colon (short bowel syndrome).
  • Colon tumors: both malignant and benign colon tumors can lead to chronic changes in bowel habits. Gastrointestinal lymphoma is also a common cause of chronic diarrhea. 
  • Other endocrinal diseases such as Addison’s syndrome and hypoparathyroidism
  • Rare intestinal diseases such as Whipple’s disease, Tropical Sprue, VIPoma, gastrinoma, carcinoid syndrome.
  • Cystic fibrosis.
  • Mesenteric ischemia.
  • Radiation therapy on the abdomen (radiation enteropathy).

MORE: 9 Causes of Diarrhea Every Day (But not Sick) & When to Worry.