Approved by the Cancer.Net Editorial Board, 02/2016

Diarrhea is frequent, loose, or watery bowel movements. If you experience diarrhea during cancer treatment, talk with your doctor. Your doctor can recommend ways to manage it. Relieving side effects is an important part of cancer care and treatment. This is also called also called symptom management or palliative care.

Causes of diarrhea

Chemotherapy, radiation therapy to the pelvis, the cancer itself, or conditions unrelated to the cancer can cause diarrhea. Other reasons that a person with cancer might have diarrhea include:

  • Taking antibiotics

  • Infection with a diarrhea-causing bacteria called Clostridium difficile

  • Removal of a portion of the bowel, because the area of bowel that reabsorbs water from foods is shorter

  • Cancer that affects the pancreas, causing greasy stools with a bad odor because the pancreas cannot absorb fat well

  • Graft-versus-host-disease, a side effect from a stem cell transplant

  • Other conditions that also cause diarrhea in people without cancer, including:

    • Irritable or inflammatory bowel disease

    • Viral infections

    • Inability to digest certain foods

The causes of diarrhea in a person with cancer vary. Your health care team may need to perform medical tests to find out the cause or causes of the diarrhea.

Grades of diarrhea

Diarrhea is described according to the following grades, from mild to severe, established by the National Cancer Institute (NCI):

  • Grade 1 is an increase of less than 4 stools a day.

  • Grade 2 is an increase of 4 to 6 stools a day.

  • Grade 3 includes several factors and you will likely need to stay in the hospital for treatment.

    •  Increase of 7 or more stools a day

    • Not being able to control bowel movements

    • Reduced ability to care for your own daily needs

  • Grade 4 is a life-threatening condition that requires immediate intensive care.

Treatment of diarrhea

Preventing diarrhea or treating it early can help you avoid dehydration or other problems. It is best to discuss your symptoms with your doctor. The best treatment for you depends on the cause of the diarrhea. The following suggestions can help you manage mild (grade 1 or 2) diarrhea:

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

  • Avoid medicines such as laxatives, metoclopramide (Reglan) to prevent vomiting and constipation, and stool softeners.

  • Eat small, frequent meals. Ask your doctor which foods are best to eat when you have diarrhea. Foods that are easy for the stomach to digest include bananas, rice, applesauce, and toast. If chemotherapy caused the diarrhea, you doctor may recommend a type of low-residue, or low-fiber, diet. You doctor may recommend other dietary changes. 

  • Drink plenty of water and other clear liquids to prevent dehydration. People with severe dehydration may need to receive intravenous (IV, through a vein) fluids.

  • For severe diarrhea from chemotherapy, ask your doctor about changing the schedule or dose.

  • Ask your doctor about medications to prevent diarrhea. The following drugs are often used for diarrhea caused by chemotherapy:

    • Loperamide (Imodium)

    • Diphenoxylate and atropine (Lomotil)

Researchers are studying drugs for preventing diarrhea caused by radiation therapy to the pelvic area. However, none have been approved yet.

More Information

Side Effects of Chemotherapy

Side Effects of Radiation Therapy

Additional Resources

NCI: Managing Chemotherapy Side Effects: Diarrhea

NCI: Managing Radiation Therapy Side Effects: Diarrhea

Lab Tests Online: Tests for Causes of Diarrhea