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How to Manage Diarrhea: For People With Cancer

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What is diarrhea?

Diarrhea is loose, watery, or unformed stool (poo) that might look like many little flakes or pieces.

Diarrhea may also:

  • happen more than 3 or 4 times a day
  • cause an urgent need to go to the bathroom 
  • start during or after your cancer treatment
  • last for a few hours or continue for a long time
  • come and go over the course of your treatment 
  • go back and forth between constipation and diarrhea, especially if you are on chemotherapy

When you have diarrhea, you may also feel:

  • bloated and have stomach cramps (pain in your belly)
  • restless or agitated (not able to stay calm or still)

Diarrhea can be a sign of a serious problem when you are on immunotherapy. 

Contact your health care team right away if you get diarrhea when being treated with immunotherapy. 

What causes cancer-related diarrhea?

Medications and treatments are the most common causes of diarrhea when you have cancer.

Some examples of medication that can cause diarrhea are:

  • chemotherapy medicines (like Irinotecan, 5-Fluorouracil (5-FU))
  • cancer surgery
  • radiation treatment to the pelvis (the area between your hip bones)
  • medications (like laxatives, antibiotics, metoclopramide, domperidone, antacids with magnesium)
  • immunotherapy (like Ipilimumab, Nivolumab)

Herbal medicines and natural health products can cause or worsen diarrhea. Some of them should not be taken when you are getting cancer treatments. Talk to your health care team before taking any herbal medicines and natural health products, especially saw palmetto, ginseng, milk thistle, plantago seed, senna, or cascara.

When should I talk to my health care team? 

Contact your health care team if you have any of the following symptoms:

  • You have diarrhea: 
    • ­more than 7 times in one day (24 hours)
    • for more than 24 hours after you have taken medication to stop it
  • Blood in your stool (poo) 
  • Pain in your abdomen (belly) that is not cramping from the diarrhea
  • You cannot eat or are afraid to eat 
  • Signs of dehydration (can be caused by diarrhea and/or vomiting): 
    • Being more thirsty than usual
    • A dry mouth and tongue 
    • Dark yellow pee or passing very little pee 
    • Fatigue (feeling very tired) or dizziness
    • Vomiting (throwing up)
    • A fast heart rate  

Go to the nearest emergency department if:

  • you have the symptoms in the list above and cannot reach your health care team
  • you develop a fever while you are getting cancer treatments. 
  • a fever is a temperature taken by mouth of:

    38.3°C (100.9°F) or higher at any time
    or
    38.0°C (100.4°F) or higher for at least one hour

What can I do to manage diarrhea?

Take medication to stop or slow the diarrhea

Your health care team may recommend taking the medication Loperamide (Imodium) to help control your diarrhea. For safety reasons, always check with your health care team before 
taking Loperamide.

Always follow your health care team’s directions for taking diarrhea medication. Your health care team may give you different directions for how to take diarrhea medication than what is written on the box of medicine. 

Drink lots of liquids to avoid dehydration

Your body loses a lot of liquid and electrolytes when you have diarrhea. Electrolytes are salts and minerals that your body needs to function properly.

To avoid dehydration when you have diarrhea:

  • Drink 6 to 8 cups of liquids a day unless your health care team has told you to drink more or less. 
  • Add an extra cup of liquid for every watery bowel movement you have.
  • Sip slowly on small amounts of liquid between meals.
  • Choose caffeine-free and non-alcoholic drinks.
  • Choose liquids with electrolytes (see next section).

Liquids with electrolytes

You can buy electrolyte drinks at the store or make them yourself. Gastrolyte and Pedialyte are good electrolyte drinks.

Sports drinks (like Gatorade) have electrolytes but they also have a lot of sugar. Dilute them with water (half water, half other liquid).

To make a homemade electrolyte replacement drink mix:

  • 6 level teaspoons of sugar 
  • Half a teaspoon of salt
  • 1 litre of tap water

Change your diet

When you have diarrhea, the following diet changes may help:

  • Eat many small meals and snacks instead of 2 or 3 large meals. 
  • Eat slowly, take small bites and chew your food well.
  • Remove all skins, peels, membranes and seeds from fruits and vegetables.
  • Limit foods that are spicy, high in fat (like deep fried foods) or anything else that bothers your stomach.
  • Ask to speak with a registered dietitian if diarrhea continues despite these recommendations.

You can start to eat normally again when:

  • you do not think food is making your diarrhea worse
  • you have not had diarrhea for about 12 to 24 hours
  • you do not need to take medications to stop your diarrhea

Take care of your skin

The skin around your bum area can be painful when you have diarrhea. To avoid sores or feeling uncomfortable, use the following tips to take care of your skin:

  • Clean your bum area with warm water and pat it dry after you go pee or have a bowel movement.
  • Use over the counter creams and ointments with zinc oxide (such as diaper cream and stoma powder) to help protect and heal the skin.
  • Caution: If you are getting radiation to the pelvis (area between the hip bones) or bum area, creams with zinc oxide may not be safe for you to use. Talk to your health care team.

Soothe the skin with a sitz bath

  • Fill your bathtub or plastic sitz bath with warm (not hot) water.
  • Add 1 to 2 tablespoons of baking soda or 1 to 2 teaspoons of salt to the water.
  • Do not add bath oils or anything else to the water.
  • Soak your bum for about 10 to 15 minutes.
  • Have as many sitz baths as you need to stay comfortable.

Key Points

  • Stop taking laxatives when you have diarrhea.    
  • Take anti-diarrhea medications as directed by your health care team.
  • Watch for signs of dehydration like thirst, a dry mouth and tongue, and dark yellow pee. 
  • Drink extra fluids and try electrolyte replacement drinks when you have diarrhea.
  • Know when to contact your health care team.

Where to Get More Information

The Canadian Cancer Society is a trusted source of information. Visit them at cancer.ca or phone 1-888-939-3333.

For more information on this symptom, or for guides to help manage other symptoms, please see Managing Symptoms, Side Effects & Well-Being.

Ontario Health’s patient guides provide Information on managing health-related symptoms (“Information”). The patient guides are for informational purposes only and are not intended to be a substitute for professional medical advice, diagnosis, treatment or care. The information does not establish a physician-patient relationship between you and Ontario Health. Always seek the advice of a qualified health care provider.

The patient guides may be amended, reproduced and distributed without prior permission of Ontario Health for limited use in health care settings where patients may benefit from the information. Ontario Health must be cited as the source only when the patient guides are reproduced in their original form. Ontario Health is not responsible for any copyright reproduction of materials.

This guide was last updated June 2025.