Approved by the Cancer.Net Editorial Board, 03/2019

Diarrhea involves frequent, loose, or watery bowel movements. Bowel movements are also called stools.

With diarrhea, you have bowel movements more often than usual. Your "baseline" is the usual number of bowel movements you have in a day.

If you have diarrhea during cancer treatment, ask your health care team about how to manage it. Relieving side effects is an important part of cancer care and treatment. This is called palliative care or supportive care.

Causes of diarrhea

Causes of diarrhea related to cancer and its treatment include:

  • Chemotherapy

  • Immunotherapy

  • Cancer that affects the pancreas

  • Radiation therapy to the pelvis

  • Removal of a portion of the bowel

  • Graft-versus-host disease, a side effect of bone marrow transplantation

Conditions unrelated to cancer that may cause diarrhea include:

  • Irritable or inflammatory bowel disease

  • Viral infection

  • The inability to digest certain foods

  • Infection with Clostridium difficile, a diarrhea-causing bacteria

  • Antibiotics

Your health care team may do medical tests to find out what is causing diarrhea.

Grades of diarrhea

Doctors use grades established by the National Cancer Institute to describe the diarrhea's severity:

Grade 1. Passing up to 4 more stools a day than a person's baseline.

Grade 2. Passing 4 to 6 more stools a day than a person's baseline.

Grade 3. This may require treatment in a hospital or clinic. It is characterized by several factors:

  • Passing 7 or more stools a day

  • An inability to control bowel movements, known as incontinence

  • Having trouble meeting daily needs without help

Grade 4. This is a life-threatening condition that requires intensive care right away.

Risks of diarrhea

Although uncomfortable, mild diarrhea usually does not cause serious problems.

But severe diarrhea can cause dehydration and electrolyte imbalances. This happens when the body loses too much water. It may also cause other health problems. To avoid such problems, take steps to prevent diarrhea or treat it early.

Prevention and treatment of diarrhea

Prevention and treatment options depend on your symptoms and the cause of diarrhea.

Ask your health care team about medicines to prevent diarrhea. These include loperamide (Imodium) as well as a combination of diphenoxylate and atropine (Lomotil). You may receive these for diarrhea caused by chemotherapy.

Researchers are studying drugs for diarrhea caused by radiation therapy to the pelvic area. But these have not been approved by the U.S. Food and Drug Administration.

Consider these options to help you manage mild diarrhea:

  • Avoid caffeine, alcohol, dairy, fat, fiber, orange juice, prune juice, and spicy foods.

  • Avoid medicines such as laxatives, stool softeners, and metoclopramide (Reglan). Sometimes, doctors prescribe metoclopramide to prevent nausea and vomiting from chemotherapy.

  • Eat small, frequent meals. And choose foods that are easy to digest. These include bananas, rice, applesauce, and toast. If chemotherapy causes diarrhea, your doctor may recommend a low-residue diet. This includes low-fiber foods.

  • Drink water and other clear liquids to prevent dehydration. People with severe dehydration may need to receive fluid through an intravenous (IV) line.

If your diarrhea is more severe or does not improve after trying the options above, contact your health care team. Depending on your symptoms, your doctor may:

  • Make changes to your diarrhea medications

  • Check your electrolytes level and/or give you IV fluids

  • Check for an infection as a cause of the diarrhea

  • Change the schedule or dosing of the chemotherapy

Sometimes, diarrhea is caused by the pancreas not working well. This happens to some people with pancreatic cancer. In such cases, replacing pancreatic enzymes may help.

Related Resources

Side Effects of Chemotherapy

Side Effects of Immunotherapy

Side Effects of Radiation Therapy

More Information

National Cancer Institute: Diarrhea

ASCO answers; Diarrhea

Download ASCO's free 1-page fact sheets on Diarrhea. This printable PDF offers an introduction to diarrhea, including the causes, risks, prevention, and treatment options. A tracking sheet on the back helps record when and how often diarrhea occurs. Order printed copies of this fact sheet from the ASCO Store.