Side effects

Fatigue

Cancer-related fatigue is a lasting tiredness that doesn't go away with rest. It is one of the most common side effects of cancer and its treatment.

What it feels like

Fatigue can make you feel tired, weak, heavy or slow, and it can make it hard to concentrate. Unlike normal tiredness, it often doesn’t get better with sleep. It may come and go, or build up over the course of treatment.

Why it happens

Many things can cause or add to fatigue, including the cancer itself, chemotherapy, radiation and other treatments, anemia, pain, poor sleep, stress or depression, not eating or drinking enough, and some medicines.

What helps

  • Stay active, gently. Short walks or light exercise, as your care team allows, can actually reduce fatigue.
  • Plan your energy. Do the things that matter most when you have the most energy, and ask for help with the rest.
  • Rest wisely. Short naps of under an hour can help, but long naps can make it harder to sleep at night.
  • Eat and drink well. Small, frequent meals and plenty of fluids help keep your energy up.
  • Look after your mood. Talking with a counselor or support group can help with stress, which often adds to fatigue.

When to call your care team

Call if your fatigue is suddenly much worse, if you are too tired to get out of bed or care for yourself, or if you also feel short of breath, dizzy or confused.

Questions to ask your care team

Bring these to your next visit, or write down your own.

  1. What might be causing my fatigue?
  2. Could anemia or another treatable problem be part of it?
  3. How much activity is safe for me right now?
  4. Would talking with a dietitian or counselor help?

Go deeper

More detailed information

For more clinical detail, our affiliate, Northside Hospital Cancer Institute, covers this topic in depth.

Fatigue and cancer treatment (National Cancer Institute)

Sources

This page is for general education and does not replace advice from your doctor or care team. Last updated October 26, 2026.

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