Why Do I Feel So Weak? Medical Causes, Treatment, and More

Medically Reviewed By Alana Biggers, M.D., MPH
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Weakness may feel like tiredness, exhaustion, or a loss of strength. It may not always accompany obvious signs of illness. Short-term weakness may occur because of overwork, stress, or lack of sleep. You may also feel weakness after overcoming an illness, such as a cold or the flu, or as a symptom of a more serious underlying condition. Weakness is also known as asthenia, which is the medical term for weakness or lack of energy or strength. It can be a broad term that describes many causes of weakness or general fatigue.

Weakness may occur throughout your entire body or in a localized area, such as your arms or legs. Weakness may also affect a single muscle or body part, such as a calf muscle.

This article will explain the possible causes of weakness, along with their symptoms and treatments. It will also discuss prevention and answer some frequently asked questions about weakness.

What causes weakness?

A man lies down on a sofa with his eyes closed.
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There are many reasons why a person may experience asthenia. Identifying the underlying cause is very important as this will help with treatment. It can also help prevent further progression or complications if it is related to illness.

Psychological conditions

Psychological conditions are commonly associated with their cognitive side effects. However, many can also cause tangible physical symptoms such as weakness or tiredness.

Psychological conditions that may cause weakness include:

Acute conditions

Some underlying medical conditions can cause feelings of weakness and fatigue.

Acute conditions may not last for long and can cause symptoms of asthenia. Some may lead to recovery without treatment or with minimal care. Severe conditions may require more treatment.

Acute conditions that may cause weakness include:

  • infection, such as the common cold or influenza (flu)
  • recovery following surgery or the use of anesthesia
  • toxicity or poisoning, such as from carbon monoxide
  • cardiovascular events, such as heart attack, stroke, or transient ischemic attack (TIA)

Chronic conditions

Chronic conditions can also lead to weakness and may require treatment. These can include:

Some chronic conditions may result in fatigue or weakness as a principal symptom, such as chronic fatigue syndrome and myasthenia.

Chronic fatigue syndrome

Weakness can be a principal clinical feature of some conditions.

Chronic fatigue syndrome (ME/CFS), also known as myalgic encephalomyelitis, is characterized by tiredness, body pain, and other symptoms.

The exact cause of ME/CFS is unknown. Clinicians believe that factors such as infection, hormonal imbalances, and genetics may lead to the condition.

Asthenia vs. myasthenia

While asthenia and myasthenia both refer to conditions involving weakness, they are different clinical disorders.

Myasthenia gravis refers to a specific autoimmune condition that causes neuromuscular symptoms including weakness of the skeletal muscles. Asthenia refers to weakness or fatigue from many different causes.

Asthenia can be a symptom of myasthenia gravis.

Learn more about myasthenia gravis here.

Behavior and lifestyle

Some behavior and lifestyle factors may contribute to feelings of weakness or fatigue. These can include:

  • drinking alcohol
  • smoking
  • exercising too little or too much
  • eating a diet that is low in nutrients or high in fat and sugars
  • consuming caffeine
  • lack of sleep or interrupted sleep
  • napping during the day
  • overworking

Side effects of medication

Weakness can also be a side effect of some medications and treatments. Examples include:

  • chemotherapy
  • radiotherapy
  • antihistamines
  • nausea medications
  • anxiety and depression medications, such as SSRIs or benzodiazepines
  • antipsychotics
  • sedatives and pain relief medications
  • some herbal remedies and supplements

Contact your doctor immediately if you experience any new symptoms while taking medication.

Always consult your doctor before using non-prescription treatments. As with all drugs, over-the-counter medications and supplements may carry the risk of side effects and negative interactions.

Aging

Weakness can be a common symptom of aging.

As you age, you may experience an unintended loss of muscle mass and strength. This process is referred to as sarcopenia.

Sarcopenia may cause you to feel fatigued. It can also increase the risk of complications such as falls, insulin resistance, and a decrease in muscle function.

Pregnancy

Pregnancy can also cause symptoms of fatigue, especially in the first 12 weeks. If you are pregnant and have fatigue that is severe, persistent, or accompanies additional symptoms, contact your doctor. Addressing these symptoms promptly can help rule out any other medical conditions.

What other symptoms might occur with weakness?

Weakness may present differently from person to person and depending on the cause. It can be accompanied by a wide variety of symptoms that may be temporary or longer-term, and can range from mild to severe.

Physical symptoms that may occur along with weakness

Primary physical symptoms occurring with weakness can include:

  • muscle aches or soreness
  • muscle spasms or cramps
  • trembling or tremors
  • persistent tiredness or sleepiness
  • slow reflexes or responses
  • difficulty carrying out daily activities
  • reduced immune system function or frequent illness
  • impaired hand-eye coordination

Other symptoms related to underlying causes may also occur along with weakness. These can include:

  • breathlessness or difficulty breathing
  • low blood pressure, particularly just after standing
  • fast heart rate or palpitations
  • loss of appetite
  • symptoms of flu such as chills or sweats, high temperature, or respiratory congestion
  • sore, swollen, or flushed skin
  • pain in the abdomen, severe pain, or a new onset of pain
  • headache
  • urinary symptoms such as increased urination or pain while urinating
  • irregular menstrual cycle or changes to your cycle
  • general feeling of being unwell
  • blurry or impaired vision

Vitamin D deficiency can also cause symptoms of weakness. Weakness from a vitamin D deficiency may occur with symptoms of bone pain, as vitamin D contributes to bone health.

Cognitive symptoms that may occur along with weakness

Weakness may occur along with emotional or cognitive symptoms, such as:

  • anxiety, irritability, or depression
  • changes in mood, personality, or behavior
  • difficulty with:
    • memory
    • thinking
    • talking
    • comprehension
    • writing or reading
  • poor concentration
  • impaired decision making
  • lack of excitement or motivation
  • sleep disturbances
  • hallucinations

When should you seek medical help?

Contact your doctor if you have any new, unexpected, or persistent symptoms of weakness. They can provide you with a diagnosis and suggest treatment if necessary.

In some cases, weakness may be a symptom of a life-threatening condition that requires immediate medical care.

Seek emergency care for the following symptoms.

Seek immediate medical care or call 911 for if you or someone else is experiencing any of these symptoms:

  • severe abdominal, pelvic, or lower back pain
  • difficulty speaking or swallowing
  • difficulty understanding speech
  • temporary changes in consciousness, such as fainting
  • seizures
  • body temperature higher than 104°F (40°C) in adults
  • incontinence or severe diarrhea or vomiting that does not improve
  • difficulty balancing, walking, or standing
  • sudden loss of vision or changes in vision
  • sudden weakness, numbness, or paralysis, particularly on one side of the body
  • severe headache
  • stiff neck

How is weakness treated?

Treatment for weakness can vary widely depending on the cause.

If weakness is due to an underlying condition, your doctor may focus on treatment methods that address the underlying condition.

Your doctor may also suggest treatments to help alleviate or manage the symptoms of weakness.

Treatment for weakness caused by acute conditions

Weakness caused by an acute condition may eventually resolve with treatment of the condition. For example, if your weakness results from a bacterial infection, treatment with antibiotics may help you recover.

Treatment for weakness caused by chronic conditions

Weakness caused by chronic conditions may require both longer-term treatment and management techniques to improve quality of life. For someone living with ME/CFS, a doctor may recommend pain and energy management techniques along with cognitive behavioral therapy.

Treatment for weakness caused by medications

If you experience weakness as a side effect of medication, your doctor may suggest making changes to your treatment. This could involve changing the dosage or switching medications.

It is important to continue taking your medication as prescribed. Do not adjust your medication yourself without consulting your doctor.

How can you prevent weakness?

It is not always possible to prevent weakness, especially if it is the result of an underlying condition.

However, maintaining a healthy lifestyle can help prevent symptoms of weakness caused by behavioral habits. It may also improve or reduce some symptoms and lower your risk for complications.

Things you can do to maintain a healthy lifestyle include:

  • maintaining a moderate body mass index (BMI)
  • not smoking
  • limiting alcohol consumption
  • eating a balanced diet
  • getting regular exercise
  • managing stress
  • getting enough good quality sleep
  • following prescribed treatment plans

Learn more about how to get better sleep here.

Other frequently asked questions

Below are more frequently asked questions about weakness.

Why do my legs feel weak?

Weakness in the legs can have many different causes.

Weakness that is unexpected or does not follow exercise may be the result of an underlying condition. Causes and conditions leading to weakness in the legs can vary widely in severity.

If you have unexpected weakness in the legs, contact your doctor promptly for diagnosis and treatment.

Why do my arms feel weak?

Weakness in the arms can be the result of many conditions, some of which may be benign or expected. It can also be a symptom of a heart attack.

Seek emergency treatment or call 911 if you have symptoms such as sudden weakness or paralysis, chest or arm pain, and shortness of breath.

Why are my hands shaking and why do I feel weak?

Hands may shake for a variety of reasons, particularly due to muscular or neurological conditions. Hand shaking may be a symptom of a tremor.

If you have shaky hands accompanied by weakness, seek prompt medical care. Getting proper diagnosis and treatment can help prevent severe complications.

Summary

Weakness or asthenia refers to feelings of physical and cognitive fatigue or loss of strength. It can be the result of a wide range of causes such as behavioral habits, side effects from medication, or underlying illness.

Some causes may be expected or easily treatable, whereas others may need more clinical attention and treatment.

Contact your doctor if you have any new symptoms of weakness or fatigue. Seek immediate medical care if you have symptoms of a stroke or heart attack such as sudden weakness or paralysis, chest pain, or confusion.

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Medical Reviewer: Alana Biggers, M.D., MPH
Last Review Date: 2022 Jul 15
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THIS TOOL DOES NOT PROVIDE MEDICAL ADVICE. It is intended for informational purposes only. It is not a substitute for professional medical advice, diagnosis or treatment. Never ignore professional medical advice in seeking treatment because of something you have read on the site. If you think you may have a medical emergency, immediately call your doctor or dial 911.