As an oncologist, I can tell you that constipation and diarrhea are some of the most common side effects patients experience during cancer treatment.
Yet they’re also some of the least discussed—largely because they feel embarrassing or “too personal”. I want to reassure you: it’s absolutely okay to talk about it.
Nothing is “too much information.”
And most importantly, these symptoms can usually be managed very effectively when your care team knows what’s going on.
Why Do Bowel Changes Happen?
Changes in bowel movements depend on many factors—your cancer type, the treatments you’re receiving, and the supportive medications we use to control pain and nausea. Here are some of the most common reasons:
• Chemotherapy
Different chemotherapy drugs affect the gut in different ways.
Some irritate the bowel or speed up motility (leading to diarrhea), while others slow things down and cause constipation.
• Immunotherapy
Rarely, immunotherapy can cause inflammation of the colon (colitis), which typically presents as diarrhea. This needs medical evaluation.
• Pain medications (especially opioids)
Opioids slow gut motility, making constipation very common.
• Antiemetics such as ondansetron (Zofran)
Higher doses especially when given before chemotherapy often cause constipation for several days afterward.
• Antibiotics
They can disrupt gut bacteria and trigger diarrhea.
• Low food and fluid intake
Loss of appetite, nausea, or dehydration can quickly worsen both constipation and diarrhea.
• Stress and anxiety
The gut–brain connection is strong. Emotional stress can significantly alter bowel habits.
Many patients experience both constipation and diarrhea at different points, sometimes even within the same week.
Let’s Talk About Diarrhea
Why Is Diarrhea Important to Report?
Diarrhea during treatment is more than an inconvenience. If not managed early, it can lead to:
- Dehydration
- Kidney injury
- Electrolyte imbalances
- Fatigue
- Fear of leaving the house due to urgency
- Reduced quality of life
For many patients, the fear of losing control in public is even more distressing than the physical discomfort.
How We Manage Diarrhea
1. Identify the cause
Your care team will ask about timing, frequency, and associated symptoms, and may check for infections like C. difficile or viral causes. A stool test may be needed.
2. Hydration, hydration, hydration
Water is important, but electrolytes are crucial—broths, electrolyte drinks, oral rehydration solutions, and popsicles all help replace what’s lost.
3. Use loperamide (Imodium) appropriately
Most patients under-dose.
Typical instructions:
- Start with 2 tablets at the first loose stool
- Then 1 tablet after each episode
- Do not exceed 8 tablets in 24 hours (unless instructed by your oncologist)
Some patients may need prescription medications like Lomotil.
4. Adjust your diet temporarily
Avoid:
- High-fiber foods (beans, corn, raw vegetables, bran)
- High-fat or greasy foods
- Dairy/lactose
- Caffeine
- Spicy foods
Focus on:
- Bananas
- Rice
- Toast
- Eggs
- Applesauce
5. When to call your oncologist
- Diarrhea lasting >24 hours
- Blood in stool
- Abdominal pain or cramping
- Fever
- Dizziness or lightheadedness
- Signs of dehydration
Let’s Talk About Constipation
Constipation is just as distressing as diarrhea—and often more silent.
Some patients think they’re “okay” because they pass small amounts of stool, but still have significant constipation.
Constipation affects 40–90% of patients with advanced cancer, depending on treatment and medications.
Why Does It Matter?
Untreated constipation can lead to:
- Pain and cramping
- Nausea or vomiting
- Early satiety and loss of appetite
- Worsening fatigue
- Rarely, bowel obstruction
How We Manage Constipation
1. Be proactive, not reactive
If you’re on opioids or anti-nausea medications, you should start a bowel regimen from day one.
2. Hydration is key (again)
Dehydration makes stools hard and more difficult to pass.
3. Incorporate bowel-friendly foods
- Prunes
- Apricots
- Figs
- Dates
- Fresh fruits and vegetables (as tolerated)
4. Gentle movement
A short daily walk can significantly improve bowel motility.
5. Use over-the-counter medications if needed
- Miralax (polyethylene glycol)
- Senna (Senokot)
- Milk of magnesia
Your team can guide you on dosing.
6. When to call
- No stool for >3 days
- No gas for >24 hours
- Severe abdominal pain, vomiting, or bloating
These may indicate a blockage and need urgent evaluation.
✅ Key Takeaway:
Constipation and diarrhea may feel embarrassing—but they are a crucial part of your cancer care.
Reporting symptoms early allows us to keep you safe, maintain treatment intensity, and help you feel more in control. There is absolutely no shame in talking about your bowel movements.
Your oncology team wants to hear about it because it helps us take better care of you.
📚References:
- Management of Severe Diarrhea in Patients With Cancer: Clinical Practice Guidelines [Webinar]. Multinational Association of Supportive Care in Cancer (MASCC); October 13, 2022.
- Benson AB III, Ajani JA, Catalano RB, et al. Recommended guidelines for the treatment of cancer treatment–induced diarrhea. J Clin Oncol. 2004;22:2918–2926.
- Andreyev J. Gastrointestinal symptoms after pelvic radiotherapy. Lancet Oncol. 2007;8:1007–1017.
⚠️Legal Disclaimer:
This information is for educational purposes only and is not a substitute for personalized medical advice. Always follow your oncology team’s instructions and discuss any changes in your treatment plan with them.