Key points
- Constipation and diarrhoea are common side effects of cancer treatment, and both can be prevented or controlled; tell your treatment team about any change in your bowel habits [1, 2].
- If you have started a strong painkiller such as morphine, start a laxative on the same day and keep taking it for as long as you take the painkiller [3, 4].
- With diarrhoea, drink plenty of fluids and eat small meals of low-fibre foods [1, 3].
- Report diarrhoea during immunotherapy the same day, even if it is mild; it may be a sign of inflammation of the bowel [7].
- 4 or more bowel movements a day above your usual number, diarrhoea at night, blood in the stools, fever or dizziness should be reported to your treatment team straight away [5, 6, 10].
Why do constipation and diarrhoea happen?
| Problem | Common causes |
|---|---|
| Constipation | Strong painkillers such as morphine; some anti-sickness medicines; some chemotherapy drugs such as vincristine, oxaliplatin and the taxanes; thalidomide; some anti-anxiety medicines and diuretics; being less active and changes in diet; the cancer itself in the abdomen or pelvis [2, 3] |
| Diarrhoea | Chemotherapy, especially irinotecan and the fluorouracil family of drugs such as capecitabine; immunotherapy (inflammation of the bowel); many targeted drugs; radiotherapy to the abdomen and pelvis; surgery on the stomach or bowel; infection; antibiotics; stress [1, 3] |
Constipation: prevention and treatment
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Start a laxative with a strong painkiller
Constipation is very common with strong painkillers and usually does not improve when the painkiller dose is lowered. That is why a laxative is prescribed at the same time as the painkiller and continued for as long as you take it [3, 4]. If you have not been prescribed one, ask for it. Read more: Cancer pain.
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Drink enough
Drink about 8 glasses of water or clear fluids a day, unless your doctor has told you to limit fluids. Hot drinks, coffee and prune juice may also help the bowel work [2].
- 3
Be active every day
Walking, an exercise bike or yoga; if you cannot walk, light exercises in bed or in a chair [2].
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Keep a routine
Eat at the same times every day and keep a record of your bowel movements to go through with your treatment team [2].
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Choose a laxative with your doctor
Common laxatives include medicines that draw water into the bowel (such as polyethylene glycol and lactulose), medicines that stimulate the bowel (such as senna and bisacodyl) and stool softeners. Take only the laxative your doctor recommends [2].
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Diarrhoea: what can I do at home?
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Small meals, low-fibre food
Eat small, frequent meals instead of three large ones. Low-fibre foods such as white bread and pasta are best. Peeled boiled potatoes, soup, bananas and crackers replace the sodium and potassium lost with diarrhoea [1].
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Avoid these
Alcohol, milk and dairy products, spicy food, caffeinated drinks, dried beans, fatty food, fruit juice, and sugar-free chewing gum or sweets [1].
- 4
Look after the skin around the anus
Clean with warm water and baby wipes, and keep the area clean and dry; sitting in a shallow warm bath can also be soothing [1].
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Keep a record
Write down how many bowel movements you have and what the stools are like. Your doctor judges how severe diarrhoea is by how many more bowel movements you have than usual [1].
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Anti-diarrhoea medicine as instructed
Talk to your doctor before taking any anti-diarrhoea medicine or supplement; your doctor may prescribe loperamide [1]. If you are having irinotecan, keep loperamide at home in advance and start it at the first loose stool, following the instructions you were given [5].
Immunotherapy drugs such as pembrolizumab, nivolumab and ipilimumab can inflame the bowel (colitis) [1, 7]. Diarrhoea may be the first sign, and colitis can become serious [7]. So:
- Report any new diarrhoea, even mild, to your treatment team the same day [7].
- Abdominal pain or blood in the stools are warning signs [7].
- This side effect usually appears a few weeks after treatment starts and is more common with a combination of two immunotherapy drugs [7].
- Ordinary anti-diarrhoea medicines are not enough to treat it, and moderate or severe cases need steroids [7].
Read more: Side effects of immunotherapy.
Medicines that need special care
Irinotecan
It can cause two kinds of diarrhoea. Early diarrhoea during or shortly after the infusion, sometimes with sweating, a runny nose, extra saliva and cramps, which the team treats with atropine. Late diarrhoea usually starts more than 24 hours after the infusion and can be dangerous; at the first loose stool or when bowel movements become more frequent than usual, start loperamide as instructed [5]. Read more: Irinotecan.
Capecitabine
If the number of bowel movements in a day goes up by 4 or more above your usual, or you have bowel movements at night, stop the tablets and call your doctor. The same applies to bloody diarrhoea with severe abdominal pain and fever [6]. Read more: Capecitabine.
When should I contact a doctor?
Call your treatment team straight away if:
- You have any new diarrhoea during immunotherapy [7].
- You have 4 to 6 or more bowel movements a day above your usual number, or diarrhoea at night [3, 6].
- Diarrhoea has not been controlled within 24 hours despite medicine [5].
- Your stools are black or bloody [5].
- You have a temperature of 38 °C or higher [10]; fever, severe cramps or nausea and vomiting together with diarrhoea make it more dangerous [3].
- You have signs of dehydration (dizziness, light-headedness or feeling faint) or cannot drink because of nausea and vomiting [5].
- You have fewer than 3 bowel movements a week, or constipation comes with severe abdominal pain, bloating and vomiting [2].
Diarrhoea of 7 or more bowel movements a day above your usual number can be life-threatening and may need treatment in hospital [1]; if you feel very unwell, call your local emergency number.
Frequently asked questions
Can I take loperamide on my own?
Talk to your doctor before taking any anti-diarrhoea medicine [1]. During immunotherapy, diarrhoea may be a sign of inflammation of the bowel and need a different treatment, so report it first [7]. If you are having irinotecan, your doctor will give you a loperamide plan in advance [5].
Which laxative is best?
Your doctor chooses the laxative according to the cause of the constipation and your situation [4]. An international guideline suggests polyethylene glycol as the first choice [4]. For constipation from strong painkillers that does not improve with the usual laxatives, there are special medicines [4].
After several days of constipation, watery stool suddenly leaks out; is it diarrhoea?
Perhaps not. Long-lasting constipation can lead to hard stool getting stuck in the bowel (faecal impaction), with watery stool leaking around it. This needs prompt medical attention; call before taking any medicine [2].
Should I stop eating when I have diarrhoea?
No. Eat small, frequent meals of low-fibre foods and drink plenty of fluids [1].
Do probiotics or fibre supplements help?
Doctors sometimes recommend probiotics or a fibre supplement; talk to your doctor before taking either [1].
Can diarrhoea delay my treatment?
Sometimes. If diarrhoea is severe, your doctor may lower the dose or pause treatment until it gets better [1]. That is why reporting diarrhoea early matters.
Related pages
Grading and management (for doctors)
Show detailsHide
| Grade | Definition |
|---|---|
| 1 | Increase of fewer than 4 stools a day over baseline; mild increase in ostomy output [3] |
| 2 | Increase of 4 to 6 stools a day; moderate increase in ostomy output; limiting instrumental activities of daily living [3] |
| 3 | Increase of 7 or more stools a day; hospitalisation indicated; severe increase in ostomy output; limiting self-care [3] |
| 4 | Life-threatening consequences; urgent intervention indicated [3] |
- Uncomplicated and complicated diarrhoea: uncomplicated = grade 1 or 2 with no other signs, managed conservatively. Complicated = grade 1 or 2 with moderate to severe cramping, grade 2 or higher nausea or vomiting, decreased performance status, fever, sepsis, neutropenia, frank bleeding or dehydration, or any grade 3 or 4 diarrhoea. Work-up: stool testing (blood, faecal leucocytes, C. difficile, Salmonella, E. coli, Campylobacter), complete blood count and electrolytes; treatment with IV fluids, subcutaneous octreotide and antibiotics [3, 9].
- Loperamide: standard therapy for uncomplicated diarrhoea [9]. Common dosing 4 mg, then 2 mg after each unformed stool, to a maximum of about 12 mg a day; it may be less effective in grade 3 or 4 diarrhoea [3].
- Irinotecan (FDA label): early cholinergic diarrhoea: atropine 0.25 to 1 mg IV or subcutaneously, prophylactic or therapeutic. Late diarrhoea: loperamide 4 mg at the first episode, then 2 mg every 2 hours until diarrhoea-free for at least 12 hours (at night 4 mg every 4 hours); these doses are not recommended for more than 48 consecutive hours because of the risk of paralytic ileus. Antibiotics for ileus, fever or severe neutropenia; for severe diarrhoea, interrupt the drug and reduce subsequent doses; delay the next weekly treatment until pre-treatment bowel function has returned for at least 24 hours without anti-diarrhoeal medicine [5].
- Octreotide: the optimal dose has not been established; start at 100 to 150 micrograms subcutaneously three times a day or 25 to 50 micrograms an hour IV, escalating to 500 micrograms three times a day, until diarrhoea-free for 24 hours [3].
- Capecitabine (FDA label): for grade 2 or higher diarrhoea (an increase of 4 to 6 stools a day or nocturnal stools), withhold the drug, then resume at the same or a reduced dose or discontinue permanently; median time to first grade 2 to 4 diarrhoea was 34 days. Before starting, test for DPYD variants unless immediate treatment is necessary [6]. DPYD and UGT1A1 testing.
- Immune checkpoint inhibitor colitis (SITC 2021): grade 1: CBC, CMP and faecal lactoferrin; grade 2 or higher: faecal calprotectin and infectious work-up (C. difficile and CMV). Endoscopy with biopsy for grade 3 or higher, or grade 2 persisting for 5 days or more. Corticosteroids from grade 2: prednisone 1 mg/kg/day for grade 2 and 1 to 2 mg/kg/day for grades 3 and 4 (grade 4 initially IV); taper within 4 weeks after improvement to grade 1 or less. No response within 3 to 5 days, recurrence on tapering or severe ulceration at colonoscopy: infliximab 5 mg/kg at weeks 0, 2 and 6; if symptoms persist after the second dose, vedolizumab 300 mg at weeks 0, 2 and 6. Test for HBV, HIV and tuberculosis beforehand, but do not wait for the results to start treatment [7].
- ASCO 2021 (general irAE principles): grade 1: continue with close monitoring; most grade 2: hold, with corticosteroids if needed; grade 3: hold and start high-dose corticosteroids, tapered over at least 4 to 6 weeks; grade 4: generally permanent discontinuation [8].
- Constipation: start a bowel regimen when an opioid is prescribed and continue it for as long as the opioid is taken; titrate the laxative to bowel function, not to the opioid dose; bulk-forming laxatives are not advised for opioid-induced constipation; avoid rectal agents in neutropenia or thrombocytopenia [3]. MASCC: polyethylene glycol as first-line treatment; peripherally acting mu-opioid receptor antagonists (PAMORAs) should always be considered in opioid-induced constipation (level of evidence I); suppositories or enemas only with stool in the rectum or descending colon that has not responded to other measures [4]. Doses: methylnaltrexone 0.15 mg/kg subcutaneously daily or every other day; naloxegol 12.5 to 25 mg orally daily [3].
Related cancer types
Related guides
References
10 referencesShow all references, 1 with a study cardClose the reference list
Numbers in the text, such as [1], refer to these sources. Sources with a “Study card” button are summarised in the site’s evidence library.
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- 8Management of Immune-Related Adverse Events in Patients Treated With Immune Checkpoint Inhibitor Therapy: ASCO Guideline Update
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This page is based on reputable scientific sources and was last updated on 28 October 2026. The content of this website is for educational and informational purposes only and does not replace consultation, diagnosis or treatment by a specialist physician. Consult your treating physician about any treatment decision.
Printed from the website; the full and up-to-date version: https://drdabiri.com/en/guides/constipation-diarrhoea-cancer/
