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Fatigue is a feeling of tiredness, exhaustion, or lack of energy. You may feel mildly fatigued because of overwork, poor sleep, worry, boredom, or lack of exercise. Any illness, such as a cold or the flu, may cause fatigue, which usually goes away as the illness clears up. Most of the time, mild fatigue occurs with a health problem that will improve with home treatment and does not require a visit to a doctor.

A stressful emotional situation may also cause fatigue. This type of fatigue usually clears up when the stress is relieved.

Many prescription and nonprescription medicines can cause weakness or fatigue. The use or abuse of alcohol, caffeine, or illegal drugs can cause fatigue.

A visit to a doctor usually is needed when fatigue occurs along with more serious symptoms, such as increased breathing problems, signs of a serious illness, abnormal bleeding, or unexplained weight loss or gain.

Fatigue that lasts longer than 2 weeks usually requires a visit to a doctor. This type of fatigue may be caused by a more serious health problem, such as:

  • A decrease in the amount of oxygen-carrying substance (hemoglobin) found in red blood cells (anemia).
  • Problems with the heart, such as coronary artery disease or heart failure, that limit the supply of oxygen-rich blood to the heart muscle or the rest of the body.
  • Metabolic disorders, such as diabetes, in which sugar (glucose) remains in the blood rather than entering the body's cells to be used for energy.
  • Problems with the thyroid gland, which regulates the way the body uses energy.
    • A low thyroid level (hypothyroidism) can cause fatigue, weakness, lethargy, weight gain, depression, memory problems, constipation, dry skin, intolerance to cold, coarse and thinning hair, brittle nails, or a yellowish tint to the skin.
    • A high thyroid level (hyperthyroidism) can cause fatigue, weight loss, increased heart rate, intolerance to heat, sweating, irritability, anxiety, muscle weakness, and thyroid enlargement.
  • Kidney disease and liver disease, which cause fatigue when the concentration of certain chemicals in the blood builds up to toxic levels.
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WebMD Medical Reference from Healthwise

Last Updated: January 07, 2013
This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.

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