Diarrhea
Diarrhea means loose or watery stools, or going more often than usual. It can lead to dehydration if it is not treated.
Why it happens
Some chemotherapy drugs, such as irinotecan, fluorouracil (5-FU), and capecitabine, often cause it. Many targeted pills, immunotherapy, and radiation to the belly or pelvis can too.
What helps
- Drink plenty of fluids, like water, broth, and oral rehydration drinks.
- Eat small meals with soft, low-fiber foods such as bananas, rice, applesauce, and toast.
- Limit dairy, caffeine, alcohol, spicy food, and greasy food until it improves.
- Use diarrhea medicine only the way your care team told you. Some chemotherapy plans say to start it at the first loose stool. If you are on immunotherapy, call before taking any.
- Keep track of how many loose stools you have each day.
- Clean the skin around your bottom gently and use a barrier cream if it gets sore.
Call your care team right away if you have
- You have 4 or more loose stools a day above your normal, or more than your team said is safe.
- You have a fever, belly pain or cramping, or blood in your stool.
- You feel dizzy or weak, or make very little urine.
- You are on immunotherapy and have any new diarrhea.
Questions to ask
- When should I start taking diarrhea medicine, and how much is too much?
- How many loose stools in a day means I should call you?
- Could this be caused by infection or by my immunotherapy?
Medicines that can cause this
- Abemaciclib
- Abiraterone
- Acalabrutinib
- Adagrasib
- Allopurinol
- Alpelisib
- Apalutamide
- Aprepitant and fosaprepitant
- Arsenic trioxide
- Asciminib
- Atezolizumab
- Axitinib
- Azacitidine
- Bendamustine
- Bortezomib
- Bosutinib
- Brentuximab vedotin
- Brigatinib
- Busulfan
- CAR T-cell therapy
- Cabazitaxel
- Cabozantinib
- Capecitabine
- Capivasertib
- Carfilzomib
- Cemiplimab
- Cetuximab
- Crizotinib
- Cytarabine
- Dabrafenib and trametinib
Sources
Quick answers
- What is diarrhea during cancer treatment?
- Diarrhea means loose or watery stools, or going more often than usual. It can lead to dehydration if it is not treated.
- Why does diarrhea happen?
- Some chemotherapy drugs, such as irinotecan, fluorouracil (5-FU), and capecitabine, often cause it. Many targeted pills, immunotherapy, and radiation to the belly or pelvis can too.
- What helps with diarrhea?
- Drink plenty of fluids, like water, broth, and oral rehydration drinks; Eat small meals with soft, low-fiber foods such as bananas, rice, applesauce, and toast; Limit dairy, caffeine, alcohol, spicy food, and greasy food until it improves; Use diarrhea medicine only the way your care team told you. Some chemotherapy plans say to start it at the first loose stool. If you are on immunotherapy, call before taking any; Keep track of how many loose stools you have each day; Clean the skin around your bottom gently and use a barrier cream if it gets sore.
- When should I call my care team about diarrhea?
- You have 4 or more loose stools a day above your normal, or more than your team said is safe; You have a fever, belly pain or cramping, or blood in your stool; You feel dizzy or weak, or make very little urine; You are on immunotherapy and have any new diarrhea.
Last updated: 2026-10-27. Medically reviewed by Veli Bakalov, MD, medical oncologist (October 2026). General education from Step by Step, the patient portal of HemeOncBuddy.