Diarrhea is a common condition that can be caused by illness or infection, or as a side effect of medicines, including many breast cancer treatments. You have diarrhea when you have loose or watery stools at least three or more times per day than you would normally expect.

Usually, diarrhea caused by breast cancer treatments can be managed with changes in diet, an antidiarrheal medicine, or a change in the dose of your treatment. But some cases of diarrhea can be severe and require a stay in the hospital.

Diarrhea can lead to other health issues, including:

  • Dehydration, in which your body doesn’t get the amount of fluids it needs
  • Malnutrition resulting from your body not getting the nutrients it needs from the foods you eat

Let your doctors know if you experience diarrhea, especially after starting a new medicine.


What are the symptoms of diarrhea?

Diarrhea can include other symptoms besides the extra trips to the toilet, such as:

  • An urgent need to use the bathroom
  • Being unable to control bowel movements
  • Cramps or pain in your stomach
  • Bloating
  • Nausea
  • Fatigue

To decide how to manage diarrhea, your care team will consider how severe it is. Diarrhea caused by breast cancer treatments can range from mild cases that can be managed at home to severe cases that need a hospital stay. Medical centers use numbers, called grades, to describe how severe a case of diarrhea is:

  • Grade 1 diarrhea is three extra bowel movements per day.
  • Grade 2 diarrhea is four to six extra bowel movements per day.
  • Grade 3 diarrhea is seven or more extra bowel movements per day. With this grade, you may have trouble caring for yourself and should be admitted to a hospital.
  • Grade 4 diarrhea is so severe that you cannot take care of yourself. This grade is life-threatening and requires immediate hospital care.
  • Grade 5 diarrhea is reported in studies and other publications if someone dies as a result of diarrhea.

With diarrhea, your body is not digesting food and drinks properly. This means diarrhea can lead to other medical conditions if it is not managed completely. The most common of these conditions are:

  • Dehydration: the body loses too much liquid. The body also loses electrolytes, minerals that are important for many physical processes. Your body needs both water and electrolytes to function well.
  • Malabsorption: the body rids itself of food and drink waste too quickly, preventing it from absorbing the nutrients it needs to work properly.

Low-grade diarrhea can be managed at home. But if you experience abdominal pain with frequent, uncontrolled bowel movements and/or bloody bowel movements, call your care team.


What causes diarrhea?

Diarrhea can result from different causes. Most commonly, it’s caused by infections, unfamiliar bacteria you might come into contact with when traveling, and reactions to certain medicines, including several treatments for breast cancer.

Medicines can interfere with the substances in your digestive tract or with your body’s ability to process food, either of which can result in diarrhea. It’s important to talk with your care team about any diarrhea you experience. Your team can suggest changes to your diet, recommend medicines to reduce diarrhea, or adjust your treatment dose if symptoms are especially challenging.

There are many breast cancer treatments that can cause diarrhea, including these treatments approved for all stages:

Medicines called bisphosphonates, which help maintain and rebuild bones, can cause diarrhea. Bisphosphonates are sometimes recommended to treat bone loss caused by breast cancer treatments including:

Bisphosphonates that may cause diarrhea include:

If you are taking a bisphosphonate and develop diarrhea, let your care team know. Since bisphosphonates aren't as likely to cause diarrhea as other treatments, your team may want to rule out other causes first.

For treatments that are approved only for metastatic breast cancer that may cause diarrhea, see the metastatic breast cancer section below.


How can I reduce my risk of diarrhea?

It's completely understandable to be worried about diarrhea as a side effect. While there isn't a lot you can do ahead of time to prevent treatment-related diarrhea, let your doctor know if you experience diarrhea. Together, you can decide on next steps.

Whenever you're starting a new medicine, ask your care team what side effects you can expect, including diarrhea. If your care team recommends neratinib, they will also recommend antidiarrheal medicine with it. But for most other treatments, your team will wait until symptoms appear before recommending you take a medicine. Ask if you should call the doctor's office if you have symptoms of diarrhea, or if you can try over-the-counter antidiarrheal medicines first.

Sometimes, making changes to your diet can help lessen the effects of diarrhea. Below, you can read tips about dietary changes you can try. Still, you may get diarrhea as a side effect of treatment, and the best action you can take is to let your doctor know.


How do I manage diarrhea?

Managing diarrhea starts with letting your care team know if you have symptoms. They can recommend changes to your diet or medicines that can treat diarrhea.

Dietary changes to ease diarrhea's effects

Since diarrhea can lead to dehydration, make sure to replace the liquid and electrolytes that you are losing. Drink plenty of water throughout the day and try to eat some salty foods such as pretzels. Some liquids that help with both water and electrolytes are:

  • Broth
  • Sports drinks
  • Clear fruit juices

You can also choose foods that may help settle your stomach or that will not aggravate your digestive tract. The foods that are part of the BRAT diet — bananas, rice, apples, and toast — are gentle on the digestive tract and likely won’t upset your stomach.

Try to avoid certain other foods that could contribute to digestive problems:

  • Spicy or greasy foods
  • Foods high in fat or fiber
  • Alcohol
  • Food or drinks high in caffeine, such as coffee and soda
  • Milk and other dairy products

Medicines for diarrhea

If diarrhea is severe enough or is caused by a breast cancer treatment that has been shown to cause severe diarrhea, your doctors may recommend a medicine to treat it, such as loperamide.

Treatment dose adjustments to lessen diarrhea

Your doctor may also consider changing the dose of your breast cancer treatment. For medicines with known side effects, there are planned options that change how much of the medicine you take or how often you take it. These are designed to make sure you are still benefitting from the treatment.

Never change the dose or frequency of your breast cancer treatment unless your doctor recommends that you do so. The most important step is to report diarrhea to your doctor. Let them know how much you are experiencing, how you feel, and how it is affecting your life. They will work with you to find an option that is best for your health.

Talk with your doctor

Communication is an important part of managing any side effect. Tell your medical team if you have any important events, such as a graduation or wedding, near the start of treatment and if there is a way to schedule treatment around them. Also let them know about your current digestive health and bathroom habits. If you have a condition such as irritable bowel syndrome, which causes episodes of diarrhea, that may affect what your team recommends for treatment.


Diarrhea and metastatic breast cancer treatment

Metastatic breast cancer (MBC) treatment can include any of the diarrhea-causing treatments listed above. There are also targeted therapies only approved to treat MBC that can cause low-grade diarrhea. These include palbociclib (Ibrance), ribociclib (Kisqali), and talazoparib (Talzenna).

It's important to replenish fluids and electrolytes if you are taking any of these medicines. Throughout the day, drink plenty of water and have some salty foods, such as pretzels. You can also try fluids that help hydrate and provide electrolytes, including broth, sports drinks, and fruit juices.

Some medicines only approved to treat MBC can sometimes cause severe, grade 3-4 diarrhea. These include the following targeted therapies:

If severe diarrhea happens, call your care team and let them know. If it's after hours, you can still call the office answering service and ask to have the on-call provider call you back.

If your care team recommends hospital care, you'll likely be given electrolytes and fluids while you're there. They may also decide to perform tests to make sure the diarrhea is not caused by an infection.

If diarrhea is very severe and difficult to control, you and your care team may decide to adjust your breast cancer treatment dose or try a different treatment.


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Reviewed and updated: May 23, 2023

Reviewed by: Evelyn Robles-Rodriguez, DNP, APN, AOCN


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