What is cancer-related fatigue?

Most people expect to feel tired during treatment. What many don’t expect is for that tiredness to continue for months, sometimes longer, after treatment ends. Cancer-related fatigue is a persistent physical, emotional or mental exhaustion that is out of proportion to what you’ve been doing, and that doesn’t go away after a good night’s sleep.

People describe it in different ways: heavy limbs, struggling to concentrate, feeling drained after a short walk or a conversation, or simply not feeling like themselves. It is one of the most common side effects of cancer and its treatment, and it can affect work, relationships and confidence. It is real, it is common, and you are not imagining it.

Why does it happen?

There is rarely a single cause. Fatigue usually builds from several things at once:

• The treatment itself. Surgery, chemotherapy, radiotherapy, immunotherapy and hormone therapies all place heavy demands on the body.
• Loss of fitness and muscle. Weeks of reduced activity during treatment mean everyday tasks take more effort than they used to.
• Disrupted sleep. Pain, hot flushes, worry and changes in routine can all affect sleep quality.
• Eating less, or differently. Changes in appetite and taste can leave you short of the energy and protein your body needs to recover.
• The emotional load. Anxiety, low mood and the effort of processing what you’ve been through are draining in themselves.
• Other medical causes. Anaemia, an underactive thyroid, infections and some medicines can all contribute, which is why it’s worth mentioning fatigue to your medical team.

Why rest alone isn’t the answer

When you feel exhausted, resting seems like the obvious response, and in the short term it helps. But long periods of inactivity lead to further loss of fitness and muscle strength. That makes everyday activity more tiring, so you rest more, and the cycle continues.

The evidence here is consistent: for many people, regular physical activity, started gently and built up gradually, is one of the most effective ways to reduce cancer-related fatigue. Activity improves heart and lung fitness, rebuilds muscle, improves sleep and lifts mood, and all of these feed back into having more energy.

The key word is gradually. Doing too much on a good day and then crashing for the next two, often called “boom and bust”, is very common. It can leave you feeling as though nothing is working.

What helps

Pace your energy

Spread demanding tasks across the day and week, with short breaks in between. Notice when your energy is usually at its best and use that time for what matters most to you. A daily routine helps more than waiting to see how you feel.

Move a little, often

Start with what feels manageable, perhaps a five or ten-minute walk, and build up slowly over the following weeks. The aim is to finish feeling you could have done a little more, not to push through exhaustion.

Protect your sleep

Keep regular sleep and wake times, get some daylight in the morning, and avoid long naps late in the day. If you do nap, 20 to 30 minutes in the early afternoon is usually enough.

Eat to recover

Regular meals that include protein, plenty of fluids, and not going too long without eating can make a noticeable difference to your energy. Read more in Eating well after cancer treatment.

Look after your mood

Fatigue and low mood often travel together. Relaxation, breathing techniques and talking about how you feel can reduce the mental load you’re carrying.

This information is general and does not replace advice from your own medical team. If you have new or worsening symptoms, contact your GP or cancer team. In an emergency, call 999.