What does change in bowel habits feel like with immunotherapy side effects?

Change in bowel habits is a common presentation of immunotherapy side effects and may include new diarrhoea, constipation, urgency, cramps, or narrower stools. The change can be mild or disruptive, and it may occur with bloating, mucus, or a feeling that you still need to open your bowels. Tell your oncology team about a new pattern, even if you are unsure whether treatment caused it.

Most people with immunotherapy side effects notice change in bowel habits as a difference from their usual routine. You might pass loose or watery stools more often, need to reach a toilet quickly, or develop abdominal soreness and cramping. Some people instead become constipated, pass hard stools, strain, or feel incompletely emptied. A change in stool shape, colour, or the presence of mucus can also be useful to report. Similar symptoms can have causes unrelated to immunotherapy, so the pattern and timing matter more than any single bowel movement.

Contact your oncology team promptly and describe when the change began, how often you are passing stool, and whether you have pain, fever, vomiting, blood, or reduced urine. Keep drinking fluids unless your care team has given you a fluid restriction. Write down medicines, laxatives, antibiotics, and foods that may have changed recently. Do not start an anti-diarrhoeal medicine or laxative, or stop cancer treatment, without advice from the team managing your immunotherapy.

Seek urgent medical help for severe or worsening abdominal pain, repeated vomiting, faintness, confusion, marked weakness, inability to keep fluids down, black stools, or visible blood. Contact your oncology service urgently for frequent watery stools, new fever, signs of dehydration such as very little urine or a dry mouth, or a swollen and tender abdomen. These symptoms can reflect inflammation of the bowel or another problem that needs assessment; do not wait for the next planned treatment visit.

Ask which symptoms should trigger a same-day call, whether you should change your diet or fluid intake, and which medicines are safe for your particular bowel pattern. You can also ask whether immunotherapy should be paused while the cause is checked and what tests might be needed. Bring a record of stool frequency, consistency, pain, temperature, and recent medicines to make the discussion more useful.