Patient information from BMJ

Fatigue: possible causes

Last published:Jun 07, 2022

Most illnesses can make you feel tired. But here we look at possible causes of long-lasting fatigue (extreme tiredness) when it is your main or only symptom.

Some conditions that cause extreme tiredness aren’t easy to cure or to treat. But there are often things that can help. And it often helps people simply to know why they feel so tired.

You can use our information to talk to your doctor about what might be causing you to feel tired, and hopefully to get some help.

What is fatigue?

Most of us feel tired at times: for example, around bedtime, or after a long day at work.

But fatigue in a medical sense means that you feel constantly exhausted, even after you have slept or rested, over several weeks or months.

It might help to think of it this way: it’s normal to feel tired for a while after doing a task or activity. But if you constantly feel that you don’t have enough energy to start a task, that’s what doctors would call fatigue.

Fatigue and medical emergencies

In this leaflet we cover the causes of long-lasting fatigue. Most things that cause this type of fatigue are not dangerous in the short term.

But there are some problems that can cause you to become very tired quite suddenly, and which need urgent treatment. These include:

• heart problems

• stroke

• some causes of anaemia

• complications of diabetes, and

• some infectious diseases, including COVID-19 (coronavirus).

If you think that your fatigue might be a symptom of a serious condition, get medical help straight away.

Diagnosing the cause of fatigue

If you see your doctor about fatigue they will ask you some questions to try to find out what is causing it. For example, they might ask about:

• your medical history and any medical problems that you have now

• any medicines you are taking

• your mental health: for example, if you feel under stress for any reason, such as problems at work or with your family

• any sleep problems

• how long you have had problems with fatigue

• whether you always feel tired or if it comes and goes

• how much activity you can do before becoming too tired

• any other symptoms you have, and

• what kind of work you do.

Your doctor might also want to examine you physically. For example, they might listen to your chest or test for any areas of tenderness.

You might also have tests, including blood tests and scans.

What are the most likely causes of fatigue?

Many health problems can have fatigue as the main or only cause. Here we look briefly at many of them.

For more detailed information on treatments for conditions that can cause fatigue, you can see our leaflets that cover most of the specific conditions listed here, including chronic fatigue syndrome, insomnia, depression, anaemia, coeliac disease, multiple sclerosis, asthma, COPD, diabetes, and heart failure.

Insomnia and other sleep problems

Sleep problems are common, and can be caused by many things, including:

• mental-health problems

• some medicines, and

• sleep-breathing problems, such as sleep apnoea.

If you are not getting enough sleep it’s not surprising that you will feel very tired for much of the time. Finding the cause of your sleep problems is important in helping you get the right treatment.

Depression, stress, and other mental-health problems

Fatigue is common among people with depression, stress, and related mental-health issues. But the link between them is not always clear.

For example, it’s often hard to say whether someone’s fatigue is caused by depression, or the other way around. Getting help with mental-health problems could help you to start to deal with both issues.

Anaemia and other blood conditions

You’ve probably heard the suggestion that if someone is tired they need more iron. This is sometimes true: a common type of anaemia is caused by low iron levels, and can be treated with iron supplements.

But other conditions that affect the blood, such as lymphoma and leukaemia, can also cause fatigue. These conditions are not common, but if you see your doctor about fatigue they will probably advise blood tests, which can rule out these problems.

A very rare cause of fatigue is heavy metal poisoning, where metals such as mercury and lead get into the blood of people working in certain industries. This is far less common than it used to be.

Heart disease

It’s not surprising that heart problems should cause fatigue, especially heart failure. Sudden fatigue, rather than chest pain, can also sometimes be the main symptom of a heart attack. This seems to be more common in women.

If you think that you have fatigue that is related to heart problems, get medical help straight away.

Hormone problems

Several problems linked to hormones can cause fatigue. These include:

• having an under-active thyroid gland. This is called hypothyroidism

• diabetes. You might not think of diabetes as a hormone problem. But people with diabetes don’t have enough of a hormone called insulin. Fatigue can be one of the early symptoms of both type 1 and type 2 diabetes

• Addison’s disease, where you don’t have enough of certain hormones. You might also hear this called primary adrenal insufficiency.

• Cushing syndrome, where you have too much of a hormone called cortisol.

Some infectious disease

Infections that can have long-lasting fatigue as one of the main symptoms include Epstein-Barr virus, HIV, COVID-19, and Lyme disease.

Medicines and other substances

Medicines can sometimes cause fatigue. These include:

• antihistamines, which are usually used to treat allergies

• many drugs for heart problems, including drugs that lower blood pressure or regulate your heart rhythm

• antidepressants

• powerful anti-inflammatories called corticosteroids, and

• drugs that control nausea (anti-emetics).

Regularly drinking a lot of alcohol, and using some recreational ('street') drugs can also cause fatigue.

Industrial toxins, such as lead used in paint, are no longer the problem that they used to be. But some toxins are still linked with fatigue. For example, metal-on-metal hip implants can leak toxins into the bloodstream.

This type of implant is rarely used now. But if you have fatigue that you think might be linked to a hip implant, talk to your doctor.

COPD and other lung problems

Chronic obstructive pulmonary disease, or COPD, is a common cause of fatigue. But other problems that affect the lungs can also cause fatigue. These include:

• sarcoidosis

• asthma, and

• pulmonary hypertension (high blood pressure in the blood vessels that supply the lungs).

Stomach and digestive problems

Problems with digestion (called gastro-intestinal problems) can cause fatigue, usually because they make it hard for you to get enough nutrition. They include:

• coeliac disease. You might also hear this called gluten intolerance.

• chronic liver disease, including cirrhosis and hepatitis

• inflammatory bowel disease, and

• irritable bowel syndrome.

Conditions that affect the nervous system

Many conditions that affect how your nervous system works can cause fatigue. Those that have fatigue as one of the main symptoms include:

• multiple sclerosis (MS). Many people with MS say that fatigue is the symptom that causes them the most difficulty

• Parkinson’s disease, and

• stroke. Almost half of people who have had a stroke will have problems with fatigue for months or years afterwards.

Problem that affect the joints

Conditions that can affect your joints, and which can also cause fatigue include:

• systemic lupus erythematosus (SLE)

• fibromyalgia, and

• rheumatoid arthritis. Doctors often don’t think of fatigue as one of the main symptoms of RA. But many people with the condition say that it bothers them a lot.

Cancer

Fatigue is a common symptom of the early stages of cancer. It often happens at the same time as other symptoms, especially losing weight without trying and depression.

Feeling tired for a few weeks doesn’t mean that you should panic and think that you have cancer. But if you see your doctor about fatigue, it can help to rule it out.

Chronic fatigue syndrome (CFS, myalgic encephalomyelitis, or ME)

CFS/ME is a long-lasting condition with symptoms that can include:

• fatigue lasting longer than six months

• memory problems

• joint pain

• headache

• not feeling refreshed after sleep, and

• feeling exhausted and unwell after even light exercise.

We don’t know what causes CFS, but it often starts after someone has a bad viral infection. CFS is hard to treat and can last for many years in some people. But it is becoming more understood, and there is more support available than in the past.

What to expect in the future

Unfortunately, some types of fatigue are hard to treat. And sometimes the cause of someone’s fatigue can’t be pinned down.

But that doesn’t mean that you have to live with feeling exhausted for long periods. Many causes of fatigue can be traced back to conditions that can be treated. And treatment can help get you back to normal.

There are other good reasons to talk to your doctor if you have fatigue. For example, fatigue could be a sign of something serious that needs treatment. And if it isn’t, then ruling out serious problems can give you some peace of mind.

It can take time to find out what causes a complex symptom such as fatigue. But talking to your doctor is a good place to start.