Lethargy is a term for when someone is experiencing an unusual lack of energy and alertness. You may have also heard lethargy referred to as fatigue.
Lethargy goes beyond just feeling tired or sleepy. It can be caused by health concerns or result from not getting enough sleep for a prolonged period or experiencing excessive stress, among other factors. When it's due to lifestyle factors, it usually gets better with rest, more sleep, eating a nutritious diet, and staying active. However, it can stick around for a long time, especially if it's linked to illness.
There are times when lethargy is normal, like if you're recovering from an illness like the flu. But lethargy can also be a sign of something more serious and should be brought to your healthcare provider’s attention.
Lethargy is a state of exhaustion, beyond a normal feeling of tiredness. If you are lethargic, you are exhausted during or after usual activities. You may not even have enough energy to start those usual activities.
Several common symptoms that are associated with lethargy include a severe lack of energy, little or no motivation, excessive drowsiness, and apathy (a lack of interest or enthusiasm). Feeling lethargic can negatively affect your reaction times, attention, concentration, short-term memory, and judgment.
Depending on what that underlying cause is, you may have other symptoms that accompany your lethargy and that are specific to the cause.
What Causes Lethargy?
Lethargy has a wide range of causes. It can be a normal response to physical activity, emotional stress, boredom, or lack of sleep. Less often, lethargy can be a symptom of a serious underlying health condition.
Lethargy may be a symptom of almost any medical condition, including:
- Depression or grief
- Iron deficiency
- Insomnia, obstructive sleep apnea, and other sleep disorders
- An underactive or overactive thyroid gland (called hypothyroidism and hyperthyroidism, respectively)
- Autoimmune diseases
- Cancer
- Diabetes
- Heart failure
- Traumatic brain injury
- A sleep disorder such as narcolepsy or insomnia
Certain medicines may also cause lethargy. These include:
- Sedatives: A type of prescription medication that slows your central nervous system
- Antidepressants: A type of prescription medication that is commonly used to treat depression and anxiety
- Antihistamines: An over-the-counter or prescription medication used to block your body from making histamines, which usually occurs when you are exposed to an allergen
- Beta blockers: These prescription medications are used to block adrenaline in your body, ultimately slowing your heart rate
- Sleeping pills: These prescription medications are used to help you sleep, but they can also cause excessive drowsiness outside of sleeping
- Diuretics ("water pills"): A type of prescription medication that helps your kidneys eliminate water and sodium from your body
Using alcohol or drugs can also cause lethargy.
When symptoms of lethargy last for at least six months and healthcare providers can find no specific cause, that’s usually when the lethargy is classified as chronic fatigue syndrome. Chronic fatigue syndrome, or myalgic encephalomyelitis, is a disabling condition that causes extreme, prolonged exhaustion and that has no cure.
Lethargy is a symptom rather than a condition, so the diagnostic process involves identifying what is causing it and treating the underlying cause. Since there are many conditions and lifestyle factors that can cause lethargy, your healthcare provider will likely start with a broad assessment.
To start, your provider will likely ask for a full medical history, including a list of medications you're currently taking. They will also perform a physical exam, including listening to your heart, checking your blood pressure and pulse, and evaluating your mental health. They may be able to identify the cause of your lethargy at this point.
Other tests may be conducted to evaluate your physical and mental health, including blood, stool, or urine tests, and various types of diagnostic imaging (such as magnetic resonance imaging, or MRI).
How to Treat Lethargy
No matter what’s causing your lethargy, feeling overly tired can disrupt your life. Fortunately, assuming your fatigue isn’t caused by a health condition that requires a professional course of treatment, there are some home remedies you can try to help reduce your fatigue.
At-home options for reducing lethargy include:
- Ensuring you’re getting adequate sleep
- Eating a healthy, well-balanced diet
- Hydrating throughout the day
- Exercising regularly
- Practicing yoga or meditation
- Removing stressors from your life
- Avoiding alcohol, smoking, and drugs
Depending on the cause of your lethargy, you can also consider taking a multivitamin or switching your medications. But make sure to consult a healthcare provider before making changes like these.
If your lethargy is caused by a health condition that can be managed or treated, a healthcare provider can discuss options for treating the root cause, as well as for managing the lethargy in the meantime.
If you’re unsure whether your lethargy is in response to a lifestyle change like stress or lack of sleep or a sign of an underlying health condition, consider talking with a healthcare provider. Fatigue is a common reason people visit their providers. In fact, an estimated 5–10% of all primary care visits are directly related to fatigue.
You should prioritize a visit to a healthcare provider if you are fatigued and experiencing any of the following:
- Confusion
- Feeling dizzy
- Blurred vision
- Sudden weight gain or loss
- Depression and thoughts of harming yourself
- Constant headaches
- Insomnia
- Constipation
- Dry skin
- Intolerance to the cold
Based on your symptoms, health history, and lifestyle habits, your doctor may run blood, kidney function, liver function, and urine tests to determine the cause of the lethargy.
Babies and Children With Lethargy
Lethargy is a common reason infants are brought to the emergency room. If your baby, or child, seems lethargic, call your provider. The provider can help determine whether the level of tiredness is nothing to worry about or a sign of a health problem like:
- Group B strep
- Chronic fatigue syndrome
- Dehydration
- Congenital heart defects
A Quick Review
Lethargy, or fatigue, is the state of feeling drowsy, unusually tired, or not alert. There are many causes of lethargy that range in severity. Some are obvious: you may feel fatigued after playing sports or if you haven’t slept well. Other causes may include illnesses or infections, such as diabetes, anemia, or cancer.
If home care remedies, including rest, don’t seem to help your lethargy—or if it’s paired with symptoms like headaches or depression—call a healthcare provider so you can determine what is causing the exhaustion and how to best manage it.
