Fatigue During Cancer Radiation Therapy

Why you're so tired after radiation therapy

When you undergo radiation therapy to treat cancer, your healthcare provider may provide you with a list of possible side effects of treatment. Things like nausea, diarrhea, and hair loss usually catch a person's attention first because they seem to be the worst. 

However, fatigue is one of the most common side effects. A lack of energy and excessive tiredness is common for cancer patients no matter their therapy, but those undergoing radiation therapy experience fatigue more frequently. It also worsens as treatment continues. 

This article reviews symptoms of fatigue, why radiation causes it, tips to manage and cope with fatigue, and when to call your healthcare provider

Prevalence of Cancer Related Fatigue

About 50%–90% of cancer patients worldwide experience cancer-related fatigue.

man laying on a couch
John Fedele  / Getty Images

Symptoms of Fatigue

The following symptoms begin after a week or so of the first radiation treatment:

  • Feeling tired or lethargic throughout the day 
  • Exhaustion (lasts longer than being tired, is more intense, and isn't relieved by rest)
  • Reduced energy
  • Reduced motivation
  • Stress
  • Inability to concentrate
  • Brain fog (mental fatigue)
  • Pain
  • Short term memory problems
  • Nausea

Walking from the parking lot to your office may take longer and it may be difficult to accomplish physical tasks. Fatigue can be extremely frustrating because you aren't quite sleepy, but you just don't have enough energy to do much.

Fatigue does affect everyone differently. Some may experience mild fatigue, while others may suffer from severe chronic fatigue that affects their quality of life considerably. Your fatigue may increase over time as you undergo more radiation therapy treatments.

Why Does Radiation Therapy Cause Fatigue?

Fatigue occurs during radiation therapy because the body is working hard to repair the damage caused to healthy cells during treatment. The degree of fatigue generally varies depending on the amount of tissue irradiated, as well as the location.

Radiation therapy may not be the sole culprit of fatigue. Fatigue also is a symptom of cancer itself and the mental stress associated with being a cancer patient. Certain medications, such as those to prevent and treat nausea, can also be responsible for fatigue. It's not always possible to pinpoint the exact cause because there are many factors in cancer treatment.

10 Tips to Help Cope With Fatigue

The following tips can help you prevent or cope with cancer fatigue:

  • Ask for and accept help: Pushing yourself to accomplish everyday chores such as cleaning, shopping, or mowing the lawn can leave you more exhausted. Ask or allow friends and family to help; they are usually happy to do so. 
  • Get plenty of sleep: If you have trouble sleeping at night, try to keep a consistent sleep schedule, have a relaxing bedtime routine, keep your bedroom cool, and limit naps to 30 or 45 minutes during the day. 
  • Rest when you need it: If you feel tired, stop and take a few moments to rest to recharge your batteries. Resting can mean taking a short power nap or just sitting in a relaxing place and taking time out for yourself.
  • Eat a healthy diet: Not having the proper amount of nutrition is the reason for 40% of radiation fatigue. Talk with your healthcare provider or nutritionist about the right amount of vitamins, minerals, proteins, and carbohydrates that are best for you.
  • Stay hydrated: Dehydration is a common cause of fatigue. Make sure you drink plenty of water and eat foods high in water content. If you are experiencing nausea, room temperature water may be easier to tolerate than water that is very cold.
  • Try to avoid caffeine: Caffeinated drinks can act as a diuretic and cause dehydration. The energy boost from caffeine is short-lived, and you may feel more tired later.
  • Avoid energy drinks: Energy drinks may give you a boost but can increase fatigue after you come down from the caffeine/sugar rush. They can also lead to dehydration, increased heart rate, anxiety, and trouble sleeping.
  • Exercise when you can: Mild exercise can increase energy. It can include a short walk, swimming, dancing, and massage. You don't have to hit the weights to reap the benefits of exercising.
  • Reduce stress: Stress reduction is different for everyone. It might include group therapy, relaxation training, yoga, or art therapy.
  • Try complementary and alternative medicine (CAM): Talk with your healthcare provider about the possibility of CAM therapy. Recent studies show some success with acupuncture, yoga, vitamin infusions, aromatherapy, reflexology, and more.

When to See Your Healthcare Provider

Many people underestimate fatigue and fail to discuss it with their practitioner. Severe fatigue that does not resolve with the tips above should be reported to your healthcare provider.

There can be underlying medical reasons for fatigue, such as anemia, that may need to be addressed. Your healthcare provider may be able to determine what is contributing to your fatigue and offer solutions.

Call your healthcare provider if you experience the following symptoms:

  • Memory problems, confusion, or brain fog
  • Can’t get out of bed
  • Severe pain
  • Ongoing depression or anxiety
  • Increased shortness of breath
  • Severe nausea, vomiting, diarrhea, or loss of appetite
  • Insomnia (trouble sleeping)


Fatigue is different from regular tiredness. It is not related to increased activity levels, it can interfere with activities of daily living, and it does not resolve with sleep or caffeine. 

Radiation therapy causes fatigue because the body is working so hard to repair the damage that treatment has caused. Symptoms include exhaustion, mental fatigue, pain, nausea, short-term memory problems, and more.

Asking for help and self-care are important for coping with fatigue. Self-care includes nutrition, rest, mild exercise, stress reduction, and hydration. Fatigue can be a result of underlying problems such as anemia or malnutrition. Talk with your healthcare provider if you are experiencing severe symptoms of fatigue.

A Word From Verywell

Fatigue is a frustrating symptom for those undergoing radiation therapy. Suddenly experiencing these limitations can impact your emotional and mental well-being. Try to be easy on yourself and keep in mind that it usually resolves a few months after treatment ends.

Talk with your healthcare provider if the tips in this article don’t help or if fatigue is affecting your quality of life.

Frequently Asked Questions

  • How long does fatigue last after radiation?

    Radiation fatigue typically goes away within one to two months of the end of treatment. However, some patients report that it takes up to 12 months. This variation may be due to treatments they are receiving along with radiation. Surgery, chemotherapy, and emotional healing can all affect fatigue.

  • How long does it take to feel normal after radiation?

    Most side effects from radiation therapy resolve within a couple of months of treatment ends.This can vary based on the person, other types of cancer treatment, and underlying causes.

10 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  6. Sleep Foundation. Why is sleep hygiene important?

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Additional Reading

By Brandi Jones, MSN-ED RN-BC
Brandi is a nurse and the owner of Brandi Jones LLC. She specializes in health and wellness writing including blogs, articles, and education.

Originally written by Lisa Fayed