Chemotherapy and Diarrhea: Causes, Care, and When to Seek Help

Yes, chemotherapy can cause diarrhea, and there are practical steps you can take to manage it safely and effectively. ^[1] Chemotherapy medicines can irritate and damage the lining of the intestines, speeding up bowel movements and reducing absorption of water and nutrients, which leads to loose or watery stools. ^{[2] [3]}

Why chemotherapy can cause diarrhea

• Direct effect on gut lining: Some chemotherapy drugs injure the cells that line the intestines, resulting in faster transit and watery stools. ^[2]
• Other medicines contribute: Common supportive drugs like anti‑nausea medicines, antibiotics, and certain antacids can disrupt the normal gut balance and trigger or worsen diarrhea. ^[2]
• Risk of dehydration and malabsorption: When stools move quickly, the body absorbs fewer fluids, vitamins, and minerals, increasing the risk of dehydration and weight loss. ^[3]

How to cope right away

• Hydrate generously: Aim for about 8–12 cups (2–3 liters) of fluid per day, including water and electrolyte drinks (e.g., oral rehydration solutions, sports drinks, broths, diluted juices). ^{[1] [4]}
• Use over‑the‑counter loperamide if allowed: Unless your care team has told you not to, loperamide (Imodium) is commonly used for chemotherapy‑related diarrhea. ^[1]
• Pause laxatives and stool softeners: Avoid these for at least 12 hours or until diarrhea stops, as they can worsen symptoms. ^[1]

What to eat and avoid

• Start with clear liquids during flares: Water, clear broths, and pulp‑free juices can be easier to tolerate initially. ^{[4] [5]}
• Choose low‑fiber, gentle foods: As symptoms improve, add bananas, white rice, applesauce, toast, rice porridge/congee, and other easy‑to‑digest foods. ^{[4] [6]}
• Eat small, frequent meals: Smaller portions are easier on sensitive intestines. ^[5]
• Avoid triggers: Limit spicy foods, high‑fiber items (whole grains, raw vegetables), very fatty foods, and sometimes dairy if lactose worsens symptoms. ^{[7] [5] [6]}
• Replace electrolytes: Consider foods and drinks with sodium and potassium (e.g., sports drinks, broths, orange juice, tomatoes, peaches) as tolerated. ^[6]

Medicines and special cases

• Loperamide is first‑line for many regimens: It helps slow bowel movements and reduce urgency. ^[1]
• Irinotecan‑related diarrhea: Early sudden cramping/diarrhea may be treated with atropine; late‑onset diarrhea is typically treated with loperamide, with escalation (e.g., diphenoxylate‑atropine or octreotide) if not improved within 48 hours according to local protocols. ^[8]
• Follow your team’s guidance: For persistent or severe symptoms, clinicians use stepwise algorithms to escalate care and evaluate other causes. ^{[9] [10]}

When to contact your care team urgently

• Frequent or persistent diarrhea: More than 3–4 times in a day, lasting over 24 hours, needs attention. ^[3]
• Six or more loose stools a day for over two days, or if symptoms interfere with daily activities. ^{[11] [12]}
• Red flags: Blood in stool, fever, new or worsening abdominal cramps lasting more than a day, signs of dehydration (dizziness, weakness), or weight loss after diarrhea begins. ^{[13] [11] [14]}
• If on oral chemotherapy: Always call before continuing pills if diarrhea develops to ensure safety. ^{[12] [15]}
• Don’t start new over‑the‑counter medicines without checking with your oncology team during active chemotherapy, because some can be unsafe in this setting. ^[16]

Practical daily tips

• Sip fluids throughout the day and consider one cup after each loose stool to keep up with losses. ^[4]
• Room‑temperature foods may be better tolerated than very hot or cold items. ^[5]
• Rest after meals for a short period to help slow digestion and reduce urgency. ^[17]
• Track symptoms: Note frequency, timing, and triggers to share with your team, which helps tailor treatment. ^{[9] [18]}

Summary

Diarrhea is a known side effect of many chemotherapy regimens, driven by irritation of the intestinal lining and medication effects, but it is often manageable with hydration, diet adjustments, and safe anti‑diarrheal medicines like loperamide when approved by your care team. ^{[2] [1]} If symptoms are frequent, persistent, or accompanied by warning signs such as fever, blood, or dizziness, contact your oncology team promptly for individualized care and possible prescription treatments. ^{[11] [13] [8] [9]}