About bowel late effects

Late effects are side effects that do not go away, or that start months or years after treatment. The most common late effect of bowel cancer treatment is a change in how the bowel works. Most people have bowel changes after surgery or radiotherapy for bowel cancer (colon, rectal or anal cancer).

Your bowel habits may not go back to the way they were before treatment. But over time, bowel symptoms usually become easier to live with. Most people find they get into a new routine that becomes normal for them. This can take 1 year or more.

If you have ongoing bowel problems, many things can help. Your doctor or specialist nurse can give you advice.

Symptoms of bowel changes

Possible symptoms of late effects to the bowel include:

bleeding from the rectum (back passage) – after radiotherapy only
passing mucus (a clear, sticky substance) from the rectum
cramps or spasms in the bowel, which may be painful
difficulty emptying the bowel completely and needing to return to the toilet quickly
feeling that you need to pass stools (poo) even when your bowel is empty – this is called tenesmus
diarrhoea
constipation
needing to rush to empty your bowel (urgency)
problems controlling your bowel, causing incontinence (leakage or soiling)
passing a lot of wind, or losing control of passing wind.

Diarrhoea

Many people find changing their diet and taking anti-diarrhoea drugs stops diarrhoea. But if this does not help, ask your doctor to refer you to a gastroenterologist. Lots of different things can cause diarrhoea, and a gastroenterologist can do a full assessment.

After bowel cancer treatment, particularly pelvic radiotherapy, some people have diarrhoea caused by changes to the small bowel, such as:

bile acid malabsorption – also called bile acid diarrhoea
small bowel bacterial overgrowth – also called small intestinal bacterial overgrowth (SIBO).

Bile acid malabsorption

Bile acids are made in the liver. They go to the small bowel when you eat, where they help digest fats. When the bile acids reach the far end of the small bowel, they are absorbed back into the body.

Sometimes radiotherapy for bowel cancer damages the small bowel. Or part of the small bowel may be removed during surgery. If the small bowel cannot re-absorb the bile acids, this can cause watery diarrhoea, painful cramping and bloating. This is called bile acid malabsorption or bile acid diarrhoea.

Your doctor may advise you to start the following treatments, to see whether symptoms improve:

Eat a low-fat diet – a dietitian will help you do this in a balanced way.
Take anti-diarrhoea drugs.
Take drugs that reduce the effect of bile acids on the bowel. The drug most commonly used is colestyramine (Questran^®, Questran Light^®). It is a powder that you mix with water or fruit juice. If colestyramine does not work, your specialist may prescribe a tablet called colesevelam (Cholestagel^®).

A SeHCAT scan can help diagnose bile acid malabsorption. Your doctor can explain more about this test. SeHCAT scans are not widely available and may not be needed.

Most people with bile acid malabsorption do not absorb enough vitamins and need to take vitamin supplements. Your doctor can talk to you about this.

Small bowel bacterial overgrowth

The large bowel contains lots of healthy or ‘good’ bacteria. These help digest food. But a healthy small bowel contains almost no bacteria. After pelvic radiotherapy, bacteria are sometimes found in the small bowel. This is called small bowel bacterial overgrowth or small intestinal bacterial overgrowth (SIBO). It can cause symptoms including:

diarrhoea
wind
bloating
constipation
nausea (feeling sick)
vomiting (being sick)
bad breath.

A breath test can help to find out whether you have small bowel bacterial overgrowth. You have the test as an outpatient. Samples of your breath are tested for signs of bacteria in your small bowel.

Small bowel bacterial overgrowth is usually treated with antibiotics.

Constipation

If you have problems with constipation after treatment, the following tips may help:

include more fibre in your diet
drink at least 1 to 2 litres (2 to 3½ pints) of fluid a day
do daily exercise, such as walking
get into a toilet routine
use the correct toilet posture – this means sitting on the toilet in the right position
check with your doctor whether you are taking medicines that can cause constipation
take medicines to treat constipation.

If the constipation gets worse or you have severe tummy (abdominal) pain, get advice from your doctor or nurse.

We have more about how to manage bowel problems, such as constipation. This includes information about diet, toilet routine, toilet posture and medicines and constipation.

Tenesmus

Tenesmus is the feeling that you need to go to the toilet but your bowel is empty.

Tell your doctor or nurse if you have these symptoms.

Difficulty emptying the bowel

After rectal surgery, some people have problems emptying their bowel completely. Signs of this can include:

feeling there is still something in your bowel after you have passed a stool (pooed)
having smaller, pellet-like stools (fragmented poo).
leakage of stool after you go to the toilet
needing to go back to the toilet several times after a bowel movement.

What can help will depend on the exact cause of your symptoms. Your doctor or continence adviser may suggest:

a toilet routine
using the correct toilet posture – this means sitting on the toilet in the right position
pelvic floor exercises
changes to your diet
medicines to treat constipation
anti-diarrhoea medicines if your stools are too soft
bowel or colostomy irrigation.

We have more information about how to manage bowel problems, such as constipation. This includes information about diet, toilet routine, toilet posture and medicines that can help.

Bowel or colostomy irrigation

This is a way of emptying the bowel by introducing warm water into it. You should only use bowel or colostomy irrigation if a healthcare professional recommends it.

Bowel or colostomy irrigation means you can completely empty your bowel at a time that suits you. After irrigation, you will be less likely to have leakage or incontinence. If you have a stoma, it will be less likely to become active at inconvenient times.

You place a narrow, flexible tube (catheter) into your rectum or stoma. You then put water through the tube. You usually do this every day or every other day. It takes about 30 minutes.

Your continence adviser or stoma care nurse can tell you more about bowel or colostomy irrigation. If it is suitable for you, they can teach you how to do it. They will also arrange for you to get the equipment you need on prescription.

Some people find bowel or colostomy irrigation too time-consuming. But others feel more in control of their bowel and more confident as a result.

Wind

If you have problems with wind after bowel cancer treatment, the following tips may help:

Cut down on foods and drinks that are causing wind.
Eat your meals at the same times each day.
Do not eat and drink at the same time.
Use pelvic floor exercises to strengthen the muscles used for bowel control.
Ask your doctor for advice if you take medicines that cause wind, such as Lactulose^® or Fybogel^®.
Some people find taking peppermint oil or eating live yoghurt can help.

Tell your doctor if wind is a problem. Sometimes other things may be making wind worse – for example, constipation or bowel conditions such as diverticular disease. Wind can also be a symptom of a food intolerance or a condition called small bowel bacterial overgrowth after radiotherapy.

Bleeding from the rectum

Bleeding from the back passage (rectum) is common after pelvic radiotherapy. Most people who have this side effect only notice bleeding occasionally. For a few people, bleeding can be heavy and needs treatment.

We have more information on bleeding from the rectum after radiotherapy.

Sore or itchy skin

Ongoing diarrhoea or incontinence (leakage from the bowel) can make the skin around the anus sore. Sometimes radiotherapy for rectal or anal cancer can also make this area of skin sore or broken.

Tell your doctor or nurse if your skin is sore or passing stools (pooing) is painful. They can give you advice about looking after your skin. They may give you creams or ointments to use. They can also check your skin for signs of other problems such as haemorrhoids (piles) or fissures.

Anal fissure

After pelvic radiotherapy, the skin of the anus may become narrower and less stretchy. Sometimes a split develops in the skin of the anus. This is called an anal fissure. It can cause a sharp, intense pain when you pass stools (poo).

We have more information about anal fissures after pelvic radiotherapy.

Rarer bowel problems

Rarely, pelvic radiotherapy may cause:

Adhesions - Normally, tissues and organs inside the tummy (abdomen) are slippery and move easily as the body moves. After surgery in the abdomen, bands of scar tissue (called adhesions) may form between abdominal tissues and organs, sticking them together.
Fistulas - a fistula is an opening that forms between areas of the body that are not usually connected. Sometimes a fistula closes on its own. It can then be managed with treatment to control symptoms. If this does not happen, it may be possible to have an operation to close it.

Getting help with late effects

At your hospital follow-up appointments, your specialist will assess your late effects and how they are being managed. They will also check that there are no signs of the cancer coming back.

Talk to your cancer doctor or specialist nurse if you have:

side effects that do not go away
new symptoms or problems after treatment has ended.

You can arrange to see your cancer doctor or specialist nurse in between appointments if needed. You can also contact your GP.

Some people with late effects need help from other specialists. Your doctor or nurse can refer you to a specialist if needed. For example:

A gastroenterologist – a doctor who treats problems with the digestive system.
A colorectal surgeon – a doctor who does operations (surgery) on the large bowel.
A urologist – a doctor who treats problems with the kidneys, bladder and male reproductive system.
A gynaecologist – a doctor who treats problems with the female reproductive system.
A continence adviser – a specialist nurse or physiotherapist who gives advice and support to people with continence problems.
A sex therapist – someone who gives information and support to people with sexual problems.
A doctor or nurse who treats late effects.

A few hospitals have clinics for people with late effects. Ask your healthcare team whether there are any near you. The Pelvic Radiation Disease Association may also be able to help you contact specialists.

Work and money

If you have late effects after cancer treatment, you may find working more difficult. Some people may decide to change the type of work they do or the way they work. Others may not be able to work anymore because of the effects of cancer on their health.

If you have to stop working you may need support with money. Or you may need help with extra costs because of late effects. We have more information about work and money that you may find helpful.

Our expert money advisers can help you deal with money worries, provide information about benefits and recommend other useful organisations that can help. Call us for free on 0808 808 00 00.

Other ways to get support

After cancer or cancer treatment, it is normal for your body to feel different, and for you to feel differently about your body. If you are worried about symptoms or are struggling with your emotions, tell your doctor or specialist nurse as soon as possible. You do not have to wait until your next check-up to contact your doctor or any other health professional.

You can talk to other people facing similar challenges by joining a support group or by using social networking sites.

Join the radiotherapy and side effects forum or another forum on our Online Community.
Chat to your specialist nurse for details of cancer support groups and counselling services in your area.
Call the Macmillan Support Line for free on 0808 808 00 00 to speak to one of our cancer support specialists.

References

Below is a sample of the sources used in our late effects of pelvic radiotherapy information. If you would like more information about the sources we use, please contact us at informationproductionteam@macmillan.org.uk

S Haas, A Højer Mikkelsen, C Jensenius Skovhus Kronborg et al. Management of treatment-related sequelae following colorectal cancer. PubMed. Colorectal Disease Journal.15 August 2022. Available at https://pubmed.ncbi.nlm.nih.gov/35969031/ [accessed March 2026]

National Institute for Health and Care Excellent (NICE). Colorectal cancer. NICE guideline [NG151]. Updated December 2021. Available from: www.nice.org.uk/guidance/NG15 [accessed March 2026]

Cervantes A, Adam R, Rosello S, et al. Metastatic colorectal cancer: ESMO Clinical Practice Guideline for diagnosis, treatment and follow-up. Annals of Oncology. 2023;34(1):10-32. Available from: www.annalsofoncology.org [accessed March 2026]

A Carlile and T McAdam. The Long-Term and Late Effects of the Diagnosis and Treatment of Colorectal Cancer. Ulster Medical Journal. 2023 May. Available at https://pubmed.ncbi.nlm.nih.gov/37649914/ [accessed March 2026]