When to Worry About Changes in Bowel Habits With Immunotherapy Side Effects

Immunotherapy changes how the immune system responds to cancer. In some people, that response can inflame the bowel and cause diarrhoea, urgency, cramps, mucus, or blood. Constipation can also result from treatment, reduced activity, reduced intake, or other medicines. Bowel symptoms may have unrelated causes, so the timing, pattern, and accompanying features matter.

Tell the oncology team when the change began, how often it occurs, whether stools are watery, and whether there is pain, fever, blood, or mucus. List recent immunotherapy doses and all medicines, including laxatives and antibiotics. Do not take anti-diarrhoeal medicines or postpone treatment advice without checking first. Replace fluids as advised, especially if stools are loose or frequent.

Seek urgent medical help for severe or increasing abdominal pain, repeated vomiting, blood or black stool, fever, faintness, confusion, very little urine, or inability to keep fluids down. These signs can indicate significant bowel inflammation, bleeding, infection, or dehydration. Use the emergency contact supplied by your cancer service if symptoms escalate outside clinic hours.

Ask whether to continue, pause, or change the next treatment, which medicines are safe, and how to monitor hydration. Ask what stool changes require same-day contact and whether tests are needed to check inflammation or infection.