What Causes Lethargy?

Medically reviewed by Suzanne Falck, MD on January 26, 2018Written by Rachel Nall, RN, BSN

Lethargy is a symptom that causes you to feel sleepy or fatigued and sluggish. This sluggishness may be physical or mental. People with these symptoms are described as lethargic. Lethargy can be related to an underlying physical or mental... Read More

What is lethargy?

Lethargy is a symptom that causes you to feel sleepy or fatigued and sluggish. This sluggishness may be physical or mental. People with these symptoms are described as lethargic.

Lethargy can be related to an underlying physical or mental condition.

What are the symptoms of lethargy?

Lethargy can cause some or all of the following symptoms:

People with lethargy may act as if they’re in a daze. They may move more slowly than they usually do.

What causes lethargy?

Many kinds of acute illnesses can make you feel lethargic. This includes the flu or a stomach virus. Other physical or medical conditions can also cause lethargy, such as:

Lethargy can also be the result of mental health conditions. These include:

Lethargy can also be a side effect of taking certain medications. For example, taking narcotic medications can cause lethargy.

When should I seek medical help for lethargy?

Symptoms of lethargy may require emergency medical attention, especially if they come on suddenly. Seek emergency medical attention if you experience lethargy along with the following symptoms:

Any noticeable, marked changes in behavior accompanied by lethargy are often cause for concern. Seek immediate medical attention if you experience thoughts of harming yourself along with lethargy.

You may also want to make an appointment at your doctor’s office if you experience any of these symptoms alongside lethargy:

Lethargy in babies or young children

Babies or young children can also experience lethargy. Symptoms in babies that may need immediate medical attention include:

How is lethargy diagnosed?

Your doctor will usually take a full medical history and do a physical exam to diagnose lethargy. Obtaining a medical history includes discussing any previous medical conditions you may have had. The medical examination may include listening to your heart and lungs, checking for bowel sounds and pain, and evaluating your mental awareness.

Diagnostic testing typically depends on what the doctor suspects may be an underlying cause. For example, if your doctor suspects a thyroid disorder, they may order blood tests to determine if your thyroid hormones are high or low.

Your doctor may order imaging studies if they suspect the cause is a brain-related disorder, such as a head injury, stroke, or meningitis. The imaging studies could include a CT or MRI scan to determine if there are any abnormalities in the brain.

How is lethargy treated?

Treatment for lethargy depends upon its underlying cause. Your doctor may prescribe medications to resolve an infection or to increase thyroid hormones. They may prescribe antidepressants if your lethargy is caused by depression or another mental health disorder.

You can practice healthy habits at home to reduce the fatigue-related symptoms of lethargy. Examples include:

See a doctor if these healthy habits don’t help your symptoms go away.

Medically reviewed by Suzanne Falck, MD on January 26, 2018Written by Rachel Nall, RN, BSN

45 possible conditions

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This feature is for informational purposes only and should not be used to diagnose. Please consult a healthcare professional if you have health concerns.

Medically reviewed by Suzanne Falck, MD on January 26, 2018Written by Rachel Nall, RN, BSN
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