Chronic Diarrhea: 5 Common Causes & How to Treat

Chronic diarrhea can be caused by infections, lactose intolerance, intestinal disorders, food allergies, or long-term medication use. It may also occur with conditions such as Crohn’s disease, ulcerative colitis, celiac disease, or irritable bowel syndrome.

Chronic diarrhea may sometimes be linked to a more serious condition, including colorectal cancer, especially when it occurs with blood in the stool, abdominal pain, or unexplained weight loss. Persistent symptoms should be evaluated to identify the underlying cause.

Treatment for chronic diarrhea depends on the cause and may include oral rehydration solutions, dietary changes, probiotics, or medications. Some causes, such as lactose intolerance or medication side effects, may improve by avoiding triggers or adjusting treatment with medical guidance.

Main causes

The main causes of chronic diarrhea are:

1. Infections

Viral and bacterial infections usually cause a sudden onset of severe diarrhea along with other symptoms, such as nausea, vomiting, headache, muscle pain, fever, chills, loss of appetite, weight loss, and abdominal pain.

Parasitic infections may take longer to cause symptoms and can last longer, sometimes leading to persistent diarrhea.

These infections can result from contaminated water, raw or undercooked meat or fish, or poor hand hygiene when handling food. Commonly contaminated foods include milk, meat, eggs, and vegetables.

How to treat: Viral infections are usually treated by preventing dehydration with fluids and oral rehydration solutions. Severe cases may require IV fluids.

Treatment for bacterial or parasitic infections depends on the severity. Drinking plenty of fluids and avoiding high-fat foods, lactose, and caffeine may help, but medical evaluation may be needed to determine whether medication is appropriate.

2. Lactose intolerance

Some people with lactose intolerance do not produce enough lactase, an enzyme made in the intestine that helps digest lactose. In these cases, frequently consuming dairy products can cause persistent diarrhea.

How to treat: Reducing milk and dairy intake or choosing lactose-free milk and diary products is recommended.

Over-the-counter lactase enzyme products, such as Lactaid, may also help digest lactose and can be taken before consuming dairy products.

3. Intestinal disorders

People with intestinal disorders such as Crohn's disease, ulcerative colitis, celiac disease, or irritable bowel syndrome (IBS) may experience frequent episodes of diarrhea, nausea, and vomiting.

These symptoms may be more likely to occur after eating foods that trigger or worsen the underlying condition.

How to treat: Many of these conditions are chronic, and treatment generally focuses on controlling symptoms and the underlying disease. Medications for abdominal pain, nausea, or vomiting and oral rehydration solutions may be recommended by a healthcare provider.

Depending on the condition, certain foods may also need to be limited or avoided, such as foods containing caffeine, raw vegetables, unpeeled fruit, dairy products, oats, high-fat or fried foods, sweets, or red meat.

4. Food allergy

A food allergy is an exaggerated immune system reaction to certain foods, such as eggs, milk, peanuts, wheat, soy, fish, or shellfish. It can cause symptoms such as vomiting, abdominal pain, and diarrhea.

How to treat: Treatment depends on symptom severity and should be recommended by a healthcare provider. According to the National Institute of Allergy and Infectious Diseases (NIAID), epinephrine is the first-line treatment for food-induced anaphylaxis, while antihistamines are considered additional treatments rather than substitutes for epinephrine.

5. Long-term medication use

Long-term use of some medications, such as antibiotics, chemotherapy drugs, or magnesium-containing antacids, can cause diarrhea.

Depending on the medication, diarrhea may be persistent, especially if the medication needs to be taken every day for a long period of time.

How to treat: Talk to the healthcare provider who prescribed the medication. They may recommend adjusting the dose, temporarily stopping the medication, or switching to another option. Do not stop a prescribed medication without medical guidance.

If antibiotics are causing diarrhea, probiotics may sometimes help restore the balance of intestinal bacteria, although their effectiveness varies. If magnesium-containing antacids are the cause, a healthcare provider may recommend a different treatment.

Could it be cancer?

Although there are many more common and benign causes of chronic diarrhea, this symptom can sometimes be associated with colorectal cancer.

According to the National Cancer Institute (NCI), colon cancer can cause changes in bowel habits such as diarrhea, as well as blood in the stool, unexplained weight loss, and abdominal discomfort.

If colorectal cancer is diagnosed, treatment may involve surgery, chemotherapy, radiation therapy, immunotherapy, or a combination of treatments, depending on the location, size, and stage of the tumor.

Treatment options

What you can take for chronic diarrhea depends on the underlying cause.

A healthcare provider may recommend medications or supplements such as:

• Loperamide, to control diarrhea when certain infections or other contraindications have been ruled out

• Saccharomyces boulardii, a probiotic supplement that may be used for diarrhea associated with antibiotic use

• Nitazoxanide, for diarrhea caused by Giardia lamblia or Cryptosporidium parvum

Antibiotics, such as ciprofloxacin or another appropriate antibiotic, may be prescribed for some bacterial infections depending on the organism involved, the severity of the infection, local resistance patterns, and the person's medical history.

Read more about diarrhea medicine that your healthcare provider may prescribe.