Radiation therapy involves aiming radiation at cancer cells to damage their DNA. It can be a highly effective prostate cancer treatment but can also cause side effects involving your bowel.

About 1 in 4 people undergoing prostate cancer treatment receive radiation therapy. Two types of radiation therapy are used to treat prostate cancer:

Research suggests that every type of treatment for prostate cancer, including radiation therapy, causes numerous side effects. You can discuss these with your doctor when making treatment decisions. The side effects tend to improve over time across all treatment types.

In this article, we examine the possible short- and long-term bowel side effects of radiation therapy for prostate cancer.

Most radiation side effects begin within days to weeks after radiation treatment. Here are some of the potential short-term side effects.

Blood in stool after radiation for prostate cancer

The cells that line your rectum are extremely delicate and prone to radiation damage. Damage to these cells caused by radiation is called radiation proctitis.

Radiation proctitis can cause bleeding and blood in your stool, which has been estimated to occur in 5–20% of people receiving standard doses of radiation.

Mucus in stool after radiotherapy for prostate cancer

Slimy mucus discharge in your stool is another possible symptom of radiation proctitis. Producing excess mucus is your body’s way of protecting the lining of your bowel from damage.

Constipation after prostate radiation

Damage to tissue in your bowels can slow the passage of stool through your digestive tract and lead to constipation.

In a 2022 study, researchers found that injecting a hydrogel into the tissue between the rectum and the prostate may help reduce gastrointestinal toxicity during prostate radiation therapy.

Compared with people in the study who were treated with the hydrogel, those who were not had higher rates of gastrointestinal symptoms, including:

  • fecal urgency
  • constipation
  • diarrhea

Diarrhea and cramping

Diarrhea is a common radiation therapy side effect that can develop due to damage to the outer layer of your bowel and rectum. It usually occurs 2–3 weeks after radiation therapy.

Frequent urge to go to the bathroom

Irritation to the lining of your bowel may give you a persistent urge to have a bowel movement even when you don’t need to.

Hemorrhoids after prostate radiation

Radiation therapy might worsen hemorrhoid symptoms. People with hemorrhoids may also have a greater risk of developing gastrointestinal toxicity than people without hemorrhoids.

Flatulence and cramping after prostate radiation

Inflammation along the wall of your bowels may lead to constipation, which is associated with increased gas production and abdominal cramping.

Other symptoms

Most side effects of pelvic radiation therapy are mild and go away within weeks. But this type of radiation therapy can also lead to serious symptoms such as:

The long-term bowel side effects are similar to the short-term effects but might not appear until long after treatment.

Chronic proctitis

Chronic proctitis develops more than 6 months after the initial radiation treatment. It can cause symptoms such as:

  • rectal bleeding
  • diarrhea
  • constipation
  • a persistent feeling that you need to pass stool
  • mucus discharge

Bowel cancer

People treated with radiation therapy for prostate cancer seem to have a small risk of developing future bowel cancer.

In a 2018 review of studies, researchers found that people with prostate cancer who were treated with radiation therapy had a 36% greater chance of developing bowel cancer than people who were not treated with radiation therapy.

Short-term side effects usually appear near the end of your radiation treatment and in the following several weeks. Most short-term side effects go away within a few weeks.

Long-term side effects of radiation therapy may not appear for weeks or years after your treatment. They can last months and may never fully go away.

Here are some of the treatment options for the bowel side effects of radiation therapy.

Home remedies and lifestyle strategies

You may be able to manage your symptoms by:

  • avoiding spicy, fatty, and acidic foods
  • eating soft and bland foods
  • keeping a log of foods that make your symptoms worse
  • using a condom to avoid infections if you engage in anal sex


Over-the-counter and prescription products that may ease your symptoms include:

Medical treatment

Possible medical treatments include:

  • embolization to stop bleeding
  • blood transfusions
  • surgery

It’s important to communicate regularly with your healthcare team while undergoing treatment and to alert them of any new or worsening side effects.

Here are some frequently asked questions people have about the side effects of radiation therapy for prostate cancer.

Does radiation of the prostate affect bowel movements?

Radiation therapy can damage the cells that line your bowel, particularly your rectum. Damage to these cells can cause many side effects.

What bowel changes can occur after radiation therapy?

You may notice changes in your bowel habits after undergoing radiation therapy, such as:

  • diarrhea
  • constipation
  • mucus or blood in your stool.

Radiation therapy can be a highly effective treatment for prostate cancer, but it can also cause many side effects that affect your bowel, such as diarrhea, constipation, and rectal bleeding.

Bowel symptoms can develop days or weeks after your treatment. Late side effects can develop months or years later. Radiation therapy may also slightly increase your risk of developing bowel cancer in the future.