Diarrhea and Cancer Treatment

This page explains diarrhea during cancer treatment: when to report it, what causes it, and how it is treated.

When you have severe diarrhea, your body does not absorb enough water and nutrients. This can lead to serious problems such as dehydration, meaning not having enough water in the body. Dehydration can be life-threatening, so tell your doctor or nurse if you have diarrhea.

Signs and symptoms include soft, loose, or watery stools and going more often than normal. They also include an urgent, hard-to-control need to go, belly pain or cramps, and excess gas. Some people also have blood or mucus in the stool, feel dizzy, have a fever, or lose weight. Report blood, dizziness, fever, or weight loss right away.

Your doctor will find the cause and recommend ways to feel better. This may include medicines and foods that help decrease or stop diarrhea.

Diarrhea means having bowel movements (stools) more often than normal. The stool may also be soft, loose, or watery. It is a common side effect of many cancer treatments, such as chemotherapy, immunotherapy, and radiation therapy.

Frequent diarrhea can be a sign of some cancers or a side effect of treatment. Causes in people with cancer include:

• Certain types of cancer, especially cancers that form in the abdomen or digestive tract.
• Chemotherapy, which can destroy healthy cells that line the digestive tract along with cancer cells.
• Immunotherapy, especially immune checkpoint inhibitors, which can inflame the colon (called colitis) and lead to diarrhea.
• Radiation therapy aimed at the abdomen, pelvis, or rectum, which can damage healthy digestive tissue.
• Surgery to the esophagus, stomach, gallbladder, or bowel.
• Targeted therapy, a common cause of diarrhea for many of these drugs.
• Bone marrow or stem cell transplant, from the medicines and radiation used, or from graft-versus-host disease.

Other causes include stress and anxiety, some medicines such as antibiotics, certain supplements and herbal products, infections, and conditions like irritable bowel syndrome.

Your doctor will talk with you to figure out the severity, or grade, of your diarrhea. Grade is based on how many bowel movements you have compared with your normal number.

• Grades 1 and 2, up to six extra bowel movements a day, can usually be managed at home.
• Grades 3 and 4, seven or more extra bowel movements a day, can be life-threatening and may need treatment in a hospital.

Finding the cause is important, so you can get relief before it interferes with treatment or causes dehydration. Your doctor may ask how many bowel movements you have had, what they were like, and what you have been eating and drinking. They will do a physical exam and may use stool tests, blood tests, a urine test, or a digital rectal exam.

Treatment depends on the cause and grade. Your doctor may suggest diet changes and prescribe medicines. You may receive fluids through a vein (IV) to replace what you lost. If chemotherapy is causing severe diarrhea, your doctor may lower your dose or pause it until you feel better.

Everyday tips:

• Drink lots of fluids. Clear liquids such as water or broth replace fluids and minerals. Room-temperature liquids are easiest on the stomach. Ask your team how much to drink.
• Eat small meals. Frequent small meals or snacks may be easier than three large ones.
• Choose low-fiber foods, such as white bread, pasta, and canned fruit.
• Eat foods high in sodium and potassium, such as boiled potatoes, soup, bananas, applesauce, and crackers.
• Avoid foods that can make it worse, including alcohol, dairy, spicy foods, caffeine, dried beans, fatty foods, fruit juices, and sugar-free gum or candy.
• Keep your bottom clean and dry. Warm water and baby wipes help. A warm, shallow sitz bath can soothe irritation.
• Keep a record of your bowel movements to share with your team.

For severe diarrhea during treatment, your doctor may prescribe loperamide (Imodium) or a combination of diphenoxylate and atropine (Lomotil). They may also suggest probiotics or fiber supplements. Check with your doctor before taking these or any other medicines and supplements.

Diarrhea can be hard to deal with, both physically and emotionally. Ask your health care team for support. If you are caring for someone with diarrhea, you can help by encouraging fluids, keeping helpful foods on hand, tracking bowel movements, and asking the team when to call.

• Call 911 or go to an emergency department if bleeding from the rectum will not stop, or belly pain comes on suddenly and hard and does not let up. The American Cancer Society treats both as emergencies. Do not drive yourself.
• Call 911 or go to an emergency department if you have gone a day or more without being able to eat, or without passing urine. Do not drive yourself.
• Call your care team right away if you are having seven or more bowel movements above your usual daily number. NCI puts that at grade 3 or 4, which can be life-threatening and may need hospital treatment.
• Call your care team right away if stool turns bloody or slimy with mucus, or you feel dizzy or light-headed when you stand. NCI says to report blood, dizziness, fever or weight loss right away.
• Call your treatment team at once, whatever the hour, if loose stools come with a temperature of 100.4°F (38°C) or higher while you are having treatment. Fever during chemotherapy is an emergency, because white cells may be too low to hold an infection back, and the antibiotics cannot wait for the clinic to open (CDC). If no one answers quickly, go to an emergency department and tell them you are on chemotherapy. On immunotherapy an inflamed colon can also be behind it, and that needs looking at fast too.
• Call your care team right away if you cannot keep enough fluid down.
• Call your care team if diarrhea lasts more than 24 hours, even with up to six extra bowel movements a day. The American Cancer Society lists diarrhea for more than 24 hours as a reason to call.

Source for the emergency signs: American Cancer Society — Diarrhea.

Source for the chemotherapy fever threshold: CDC — Fever and Cancer Treatment.