Side effects
Diarrhea
Diarrhea means having loose or watery stools more often than usual. It can be caused by some cancer treatments and can lead to dehydration if it isn't managed.
Why it happens
Some cancer treatments irritate the lining of the bowel. Diarrhea can also be caused by infections, some antibiotics and other medicines, and by certain cancers.
What helps
- Drink plenty of clear fluids, such as water, broth and electrolyte drinks, sipped throughout the day.
- Eat small, frequent meals of easy foods such as bananas, rice, applesauce, toast, eggs and plain chicken.
- Limit foods that make diarrhea worse: greasy, fried or spicy foods, high-fiber foods, dairy if it bothers you, caffeine, alcohol and sugar-free products that contain sugar alcohols.
- Keep the skin around your bottom clean and use a barrier cream if it becomes sore.
- Check with your care team before taking anti-diarrhea medicine.
When to call your care team
Call if you have six or more loose stools in a day, diarrhea that lasts more than a day, blood in your stool, belly pain or cramping, a fever, or signs of dehydration such as dizziness, very dark urine or urinating very little. If you are on immunotherapy, report any diarrhea right away.
Questions to ask your care team
Bring these to your next visit, or write down your own.
- Can I take anti-diarrhea medicine, and how much?
- What should I eat and drink?
- How many bowel movements a day means I should call you?
Go deeper
More detailed information
For more clinical detail, our affiliate, Northside Hospital Cancer Institute, covers this topic in depth.
Diarrhea and cancer treatment (National Cancer Institute)Sources
This page is for general education and does not replace advice from your doctor or care team. Last updated October 26, 2026.