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Diarrhea
Diarrhea is a common symptom for many people with cancer. It can lead to serious problems or delays in treatment.
What is diarrhea?
Diarrhea is when you have more stools in a day than what is usual for you. These stools are usually loose or watery, and you might also have abdominal (belly) pain, cramping, or discomfort.
Diarrhea can lead to other problems, such as:
- Weakness
- Loss of appetite
- Dehydration
- Electrolyte changes
- Infection
What causes diarrhea in people with cancer?
Many people with cancer have diarrhea at some point.
Possible causes of diarrhea in people with cancer
- The type of cancer, such as pancreas, gastric, and colorectal
- Infections, such as Clostridioides difficile (C. diff) or neutropenic enterocolitis (typhlitis)
- Small bowel obstructions (blockages)
- Graft versus host disease (GVHD) after a bone marrow (stem cell) transplant
Cancer treatments that can cause diarrhea
- Chemotherapy (chemo), especially 5-fluorouracil (5FU), capecitabine, and irinotecan
- Immunotherapy, especially immune-checkpoint inhibitors
- Targeted drug therapy, especially tyrosine kinase inhibitors
- Radiation therapy to the abdomen (belly), pelvis, bowel, bladder, or reproductive organs
Why chemotherapy causes diarrhea
People who are treated with chemo may have diarrhea. Cancer cells grow fast, and chemo kills fast-growing cells. Because chemo travels throughout the body, it can also damage healthy fast-growing cells in the digestive tract. Diarrhea can happen as a result.
Diarrhea from chemo usually starts a few days after getting chemo. But diarrhea from immunotherapy or targeted drug therapy might start weeks or even months after treatment begins.
What are symptoms of diarrhea?
Diarrhea can be different depending on the person. It depends on what your usual stools are like. Common symptoms include:
- Frequent, loose, watery bowel movements (stools)
- Blood or mucous in stools
- Stomach pain or cramps
- Abdominal (belly) swelling or bloating
- Nausea or upset stomach
- Sudden need to have a bowel movement (urgency)
Call 911 or go to the emergency room
Call 911 or your local emergency number or have someone take you to the nearest emergency room if you:
- Have bleeding from your rectum that will not stop
- Have sudden, intense belly pain that will not stop
- Cannot pee (urinate) or eat for 1 day or more
Tests to find the cause of diarrhea
- Stool samples test for infection.
- Imaging tests, such as an x-ray or CT scan, look for inflammation or other problems.
- Blood tests check electrolyte levels and look for signs of dehydration. Both are common with diarrhea that lasts more than a few days.
How is diarrhea treated?
Managing diarrhea includes treating both the cause and symptoms.
Medicines
- Antibiotics or other medicines can help treat diarrhea caused by an infection. Many doctors also suggest avoiding antidiarrheal medicines if your diarrhea is caused by an infection because it might make the infection last longer.
- Antidiarrheals, such as Imodium (loperamide), can help treat diarrhea that is not caused by an infection.
- Steroids can treat diarrhea caused by immunotherapy.
- Fluids and electrolytes might help if you’re very dehydrated from diarrhea.
- You may need to stop constipation medicines.
Food and drinks
Try the following to help manage your diarrhea:
- A clear liquid diet: Drink water, weak tea, apple juice, peach or apricot nectar, clear broth, popsicles, or Jello. Drink these when diarrhea starts or when you feel that it’s going to start.
- The BRAT diet: Eat bananas, rice, applesauce, and toast. Start this when you’re ready to eat solid foods.
- Other foods: Try eating potatoes, noodles, pasta, cereal, boiled vegetables, and low-salt soup.
- Liquids: Drink at least 1 cup of water, sports drinks, or bouillon, after each loose bowel movement to replace the fluids you lost.
- Medicine: Take medicine for diarrhea only if and as prescribed.
Avoid eating or drinking products that can cause your diarrhea or symptoms to get worse, such as:
- Caffeine and alcohol
- Foods that upset your stomach
- Spicy foods and foods high in fat or sugar
- Acidic drinks, such as tomato juice, citrus juices, prune juice, and fizzy drinks
See Dehydration and Lack of Fluids for more information.
Are there other ways I can manage diarrhea?
Here are some other tips that might be helpful if you have diarrhea:
- Avoid tobacco.
- Avoid supplements including aloe, milk thistle, saw palmetto, ginseng, coenzyme Q10, green tea, and large amounts of vitamin C.
- Track the frequency and the amount of your bowel movements.
- Use dampened toilet paper or baby wipes to clean yourself to help soothe sore areas.
- Sit in a tub of warm water or a sitz bath to help reduce pain or discomfort.
- Apply petroleum ointment to the anal area to help soreness.
When should I talk to my doctor or cancer care team?
Make sure your cancer care team knows if you have diarrhea. It can lead to serious problems if it isn’t managed.
Tell them if you:
- Have diarrhea for more than 24 hours
- Cannot keep liquids down for more than 24 hours
- Notice any blood in your stool
- Have a fever (ask what temperature counts as a fever)
Ask your doctor or cancer care team what symptoms you should call about right away. Ask which symptoms you can wait until office hours to call about. Make sure you know who to contact when the office is closed or after business hours.
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- References
Developed by the 黑料大湿Posts Cancer Society medical and editorial content team with medical review and contribution by the 黑料大湿Posts Society of Clinical Oncology (ASCO).
Akbarali HI, Muchhala KH, Jessup DK, Cheatham S. Chemotherapy induced gastrointestinal toxicities. Adv Cancer Res. 2022;155:131-166.
黑料大湿Posts Society of Clinical Oncology (ASCO). Diarrhea. Accessed at cancer.net. Content is no longer available.
Bonis PA & Lamont JT. Approach to the adult with chronic diarrhea in resource-abundant settings. UpToDate. Updated May 22, 2026. Accessed at https://www.uptodate.com/contents/approach-to-the-adult-with-chronic-diarrhea-in-resource-abundant-settings on September 17, 2026.
Grover S, Wang Y, & Dougan M. Immune checkpoint inhibitor colitis. UpToDate. Updated May 2023. Accessed at https://www.uptodate.com/contents/immune-checkpoint-inhibitor-colitis on September 17, 2026.
Krishnamurthi SS and Macaron C. Management of acute chemotherapy-related diarrhea. UpToDate. Updated October 10, 2025. Accessed at https://www.uptodate.com/contents/management-of-acute-chemotherapy-related-diarrhea on September 17, 2026.
Krishnamurthi SS and Kamath SK. Chemotherapy-associated diarrhea, constipation, and intestinal perforation: pathogenesis, risk factors, and clinical presentation. UpToDate. Updated February 11,2026. Accessed at https://www.uptodate.com/contents/chemotherapy-associated-diarrhea-constipation-and-intestinal-perforation-pathogenesis-risk-factors-and-clinical-presentation on September 17, 2026.
Lamont JT, Bakken JS, and Kelly CP. Clostridioides difficile infection in adults: Epidemiology, microbiology, and pathophysiology. UpToDate. Updated September 3, 2026. Accessed at https://www.uptodate.com/contents/clostridioides-difficile-infection-in-adults-epidemiology-microbiology-and-pathophysiology on September 17, 2026.
National Comprehensive Cancer Network (NCCN guidelines). Management of Immune Checkpoint Inhibitor-Related Toxicities. v1. 2025. Accessed at https://www.nccn.org on September 17, 2026.
Nielsen DL, Juhl CB, Chen IM, Kellermann L, Nielsen OH. Immune checkpoint Inhibitor-Induced diarrhea and Colitis: Incidence and Management. A systematic review and Meta-analysis. Cancer Treat Rev. 2022;109:102440.
Last Revised: October 8, 2026
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