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Merck Manual

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Quick Facts

Chronic Fatigue Syndrome

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What is chronic fatigue syndrome?

Chronic is something that lasts a long time. Fatigue is tiredness. Chronic fatigue syndrome is extreme tiredness (fatigue) that lasts more than 6 months.

  • Chronic fatigue syndrome is rare, but it is most common among women aged 20 to 50

  • Doctors don’t know what causes it

  • Sometimes the symptoms start during or after a short illness, such as fever with a runny nose

  • You feel tired and lack energy, even if you get plenty of rest

  • Doctors treat chronic fatigue syndrome by easing your symptoms, and also with counseling and exercise

What causes chronic fatigue syndrome?

Doctors don’t know what causes chronic fatigue syndrome. It may run in families and may be caused by a combination of things, such as:

  • An infection caused by a virus

  • Substances you're exposed to

  • Problems with your immune system

What are the symptoms of chronic fatigue syndrome?

The main symptoms are:

  • Feeling a strong need to rest even after sleep

  • Having very little energy all day long

  • Being too tired to do daily activities

  • Tiredness that gets worse with exercise or stress

This tiredness lasts more than 6 months.

You may also have other symptoms like:

  • Trouble with focusing or sleeping

  • Sore throat

  • Headache

  • Pain in your joints, muscles, or belly area

These symptoms are similar to the symptoms of fibromyalgia.

How can doctors tell if I have chronic fatigue syndrome?

Doctors don’t have a test for chronic fatigue syndrome. They usually run blood and urine tests to rule out other diseases. If you're on any medicines, your doctor will check to see if you're having side effects from them. Doctors diagnose chronic fatigue syndrome only if they can’t find another cause that explains your fatigue.

How do doctors treat chronic fatigue syndrome?

Doctors treat your symptoms, including pain, depression, and not being able to sleep. They also try:

  • Therapy to help you focus on positive thoughts and getting better

  • A graded exercise program, in which you slowly add activities to your daily routine, such as walking, swimming, cycling, or jogging

Usually the symptoms get better over time, but it may take years or they may not go away completely.

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