What causes lethargy?

Lethargy can be a normal response to inadequate sleep, overexertion, overworking, stress, lack of exercise, or boredom. When part of a normal response, lethargy often resolves with rest, adequate sleep, decreased stress, and good nutrition. Persistent lethargy that does not resolve with self-care may be due to a variety of diseases, disorders or conditions.

Heart- and lung-related causes of lethargy

Lethargy may be caused by heart and lung problems including:

  • Asthma
  • Cardiomyopathy (weakened or abnormal heart muscle function)
  • Chronic obstructive pulmonary disease (COPD, includes emphysema and chronic bronchitis)
  • Coronary artery disease (plaque buildup in the walls of coronary arteries)
  • Heart failure (deterioration of the heart’s ability to pump blood)
  • Heart valve disease
  • Pneumonia

Psychosocial and neurological causes of lethargy

Lethargy may be caused by psychosocial or neurological conditions including:

  • Alcohol use
  • Anxiety disorders
  • Dementia
  • Depression
  • Drug abuse
  • Eating disorders
  • Grief
  • Lack of exercise
  • Overwork
  • Work shift changes

Other causes of lethargy

Lethargy can also be caused by diseases, disorders or conditions including:

Serious or life-threatening causes of lethargy

In some cases, lethargy may be a symptom of a serious or life-threatening condition that should be immediately evaluated in an emergency setting. These include:

  • Acute decompensated heart failure (rapid deterioration of the heart’s ability to pump blood)
  • Arrhythmia (abnormal heart rhythm)
  • Drug overdose
  • Electrolyte (salt) imbalances
  • Hemorrhage or internal bleeding
  • Severe depression
  • Severe infection
  • Trauma

Questions for diagnosing the cause of lethargy

To diagnose your condition, your doctor or licensed health care practitioner will ask you several questions related to your lethargy including:

  • When did you first notice your lethargy?
  • What kind of sleep are you getting?
  • How often is lethargy affecting you?
  • Do you have any stress in your life?
  • How is your mood?
  • What is your schedule like?
  • What is your diet like?
  • What kind of exercise do you get?
  • Do you have any other symptoms?
  • What medications are you taking?
  • Do you drink any alcohol or use any illicit drugs?

What are the potential complications of lethargy?

Because lethargy can be due to serious diseases, failure to seek treatment can result in serious complications and permanent damage. Once the underlying cause is diagnosed, it is important for you to follow the treatment plan that you and your health care professional design specifically for you to reduce the risk of potential complications including:

  • Abnormal menstrual periods or infertility
  • Depression
  • Drug overdose
  • Disability
  • Isolation
  • Persistent symptoms
  • Progressive heart, lung, liver or kidney disease
  • Spread of cancer
  • Spread of infection


Fatigue. Medline Plus, a service of the National Library of Medicine National Institutes of Health. http://www.nlm.nih.gov/medlineplus/ency/article/003088.htm. Accessed May 24, 2011.

Depression. Medline Plus, a service of the National Library of Medicine National Institutes of Health. http://www.nlm.nih.gov/medlineplus/ency/article/003213.htm. Accessed May 24, 2011.


What is lethargy?

Lethargy can be described as tiredness, weariness, fatigue, or lack of energy. It can be accompanied by depression, decreased motivation, or apathy. Lethargy can be a normal response to inadequate sleep, overexertion, overworking, stress, lack o... Read more about lethargyintroduction


What other symptoms might occur with lethargy?

Lethargy may accompany other symptoms that vary depending on the underlying disease, disorder or condition. Lethargy is a nonspecific symptom, so identifying other symptoms may be helpful in determining its cause.... Read more about lethargysymptoms

Medical Reviewer: All content has been reviewed by board-certified physicians under the direction of Rich Klasco, M.D., FACEP. Last Annual Review Date: May 2, 2011 Copyright: © Copyright 2011 Health Grades, Inc. All rights reserved. May not be reproduced or reprinted without permission from Health Grades, Inc. Use of this information is governed by the HealthGrades User Agreement.