Can immunotherapy cause diarrhea and how to manage it

Immunotherapy can cause diarrhea, often due to inflammation of the colon known as immune‑related colitis. This happens when immune checkpoint drugs activate the immune system and it mistakenly inflames the bowel, leading to loose, watery stools, increased stool frequency, or both. ^[1] Diarrhea from immunotherapy may signal swelling of the large intestine and should be taken seriously because it can worsen quickly if not managed early. ^[2] Some checkpoint inhibitors (PD‑1/PD‑L1 and CTLA‑4 agents) can cause severe gastrointestinal toxicity that can be life‑threatening, especially with combinations or ipilimumab; prompt recognition and correct management are critical. ^{[3] [4]}

When to call your care team

• More than 3 watery stools in a day is a threshold to call your oncology team. ^[5]
• Changes in stool appearance (becoming more liquid/watery) or new blood/mucus warrant immediate contact. ^[5]
• Do not self‑treat with anti‑diarrheal medications (like loperamide) without your provider’s guidance, because stopping diarrhea without addressing inflammation can be harmful in immune‑related colitis. ^{[5] [6]}

What you can do right away

• Hydration: Aim for 8–10 cups of fluids daily; include electrolytes (sports drinks, oral rehydration solutions, broths) to replace salts and fluids lost. ^[6]
• Diet adjustments: Choose soft, bland, low‑fiber foods; examples include white bread, pasta, rice, and refined grains. ^[7]
• Short‑term BRATT plan: You can try the BRATT diet (Bananas, Rice, Applesauce, Tea, Toast) for 1–2 days as symptoms settle, then gradually reintroduce a balanced diet. ^[7]
• Avoid irritants: Steer clear of spicy foods, high‑fat foods, alcohol, caffeine, prune/orange juice, and dairy if they worsen symptoms. ^{[6] [8] [9]}

What to avoid until you speak with your clinician

• Over‑the‑counter anti‑diarrheals or laxatives without approval, as they may mask or worsen immune‑mediated inflammation. ^{[5] [6]}
• High‑fiber and greasy foods during active diarrhea, which can aggravate symptoms. ^{[7] [8]}

Medical evaluation and treatment

Your team will evaluate severity (grade) and rule out infections, then tailor treatment:

• Mild (Grade 1): Often managed with close monitoring, hydration, and diet, with instructions to call for any worsening; your team may pause immunotherapy depending on persistence. ^[3]
• Moderate to severe (Grade 2–4): Typically requires holding immunotherapy and starting corticosteroids (such as prednisone or IV methylprednisolone) to calm bowel inflammation; this is standard for immune‑related colitis and aims to quickly control immune activity. ^{[10] [3]}
• If steroid‑refractory: Specialists may add other immunosuppressive therapies (for example, infliximab) per institutional protocols to resolve colitis safely. ^{[10] [3]}

Because immune‑related diarrhea arises from inflammation, the correct treatment is to reduce the immune response rather than simply stop bowel movements, which is why medical guidance is essential. ^{[3] [10]}

Practical daily tips

• Sip fluids often and include electrolyte drinks to replace sodium and potassium lost through loose stools. ^[6]
• Small, frequent meals (6–8 per day) can be gentler on your gut than large meals. ^[9]
• Room‑temperature foods may be easier to tolerate than very hot or cold items. ^[7]
• Probiotics may help digestion for some people, but check with your team before starting. ^[9]

Red flag symptoms needing urgent care

• Signs of dehydration (dizziness, fast heartbeat, reduced urination), severe abdominal pain, fever, blood in stool, or rapidly increasing stool frequency should prompt urgent medical attention, as immune‑related colitis can escalate. ^{[10] [3]}

Summary

• Yes, immunotherapy can cause diarrhea due to immune‑related colitis (inflammation of the colon). ^[1]
• Call your care team if you have more than 3 watery stools in a day or a change in stool appearance, and avoid self‑treating with anti‑diarrheals without guidance. ^{[5] [6]}
• Hydration, electrolytes, and bland, low‑fiber foods help symptom control, while your team decides if steroids or holding therapy is needed. ^{[7] [6] [3]}