When should you see a doctor about change in bowel habits?

A bowel change can include new constipation, diarrhoea, alternating patterns, narrower stools, urgency, or a feeling that the bowel has not emptied. Diet, infection, medicines, stress, and inflammation can cause these symptoms. A change in bowel habits is a presentation of colorectal cancer and rectal cancer, but it does not by itself establish either diagnosis.

Note the form and frequency of stool, blood or dark colour, mucus, pain, bloating, fever, appetite, and energy. If you receive immunotherapy, diarrhoea or abdominal pain may be an immune-related treatment side effect and should be reported to your cancer team rather than managed alone.

Arrange a clinical review for an unexplained change that persists, recurs, or interferes with daily life. Bring a list of medicines and describe recent diet, travel, infections, and cancer treatments. Drink appropriate fluids unless a clinician has restricted them. Avoid taking anti-diarrhoeal or laxative medicines repeatedly without advice, because the underlying cause may need assessment.

Seek urgent help for heavy rectal bleeding, black stools with weakness or dizziness, severe abdominal pain, persistent vomiting, a swollen abdomen with inability to pass stool or gas, fainting, or signs of dehydration such as confusion and very little urine. People on cancer treatment should contact their oncology team promptly for significant or rapidly worsening diarrhoea.

Ask what may be causing the pattern, whether examination or stool and blood tests are needed, and whether bowel imaging is appropriate. If you are receiving immunotherapy, ask whether treatment should be paused or adjusted and which symptoms require same-day advice.