Fatigue and asthenia: tiredness, weakness and the causes not to miss
- Topic
Feeling tired all the time is common and has many causes: anemia, thyroid problems, depression, poor sleep, diabetes and more. Here is how to sort them.
See it in 3D: Thyroid gland
What it is
Fatigue (asthenia) is a feeling of weariness or lack of energy that rest does not fully relieve. It must be separated from sleepiness (a tendency to doze, which improves with sleep), true muscle weakness (loss of strength on examination, called adynamia when the patient lacks the strength to move) and breathlessness on effort. Fatigue can be physiologic (overwork, poor sleep), secondary to an illness, or chronic (six months or more); a careful history finds most causes, and broad testing without a lead is low-yield.
Key facts
- Onset and duration: recent fatigue after an infection or life event differs from months of progressive tiredness.
- Pattern: worse in the morning and better through the day suggests depression; worse as the day goes on suggests physical disease or myasthenia; worse after effort, with long recovery, suggests ME/CFS.
- Sleep: snoring, witnessed pauses in breathing, unrefreshing sleep, shift work, insomnia.
- Mood: sadness, loss of interest, anxiety, grief; screen for depression with a validated tool.
- Systemic review: weight change, fever, sweats, bleeding or heavy periods, cold intolerance, constipation, thirst and polyuria, cough.
- Medicines and substances: sedatives, antihistamines, beta-blockers, antidepressants, corticosteroids, diuretics, alcohol and drugs.
Step by step
- Clarify the complaint: 'When you say tired, do you mean sleepy, weak, without energy or short of breath?'
- Ask about onset, duration, pattern through the day and effect on work and daily life.
- Explore sleep, mood, work load, stress and substance use.
- Go through the review of systems for red flags and for endocrine, hematologic, infectious and cancer clues.
- Review every medicine, including over-the-counter ones and supplements.
- Examine: weight and vital signs, pallor, thyroid, lymph nodes, heart and lungs, abdomen, muscle strength and reflexes.
- Order a focused set of tests; review again in a few weeks if results are normal and there are no red flags.
Causes of fatigue to consider
| Group | Clues | Example |
|---|---|---|
| Hematologic | Pallor, breathlessness on effort, heavy periods, poor diet | Iron deficiency anemia |
| Endocrine, thyroid | Cold intolerance, constipation, weight gain, dry skin | Hypothyroidism |
| Endocrine, adrenal | Weight loss, darker skin, salt craving, low blood pressure | Adrenal insufficiency |
| Metabolic | Thirst, polyuria, weight loss, blurred vision | Type 2 diabetes |
| Psychiatric | Low mood, loss of interest, early waking, worse in the morning | Major depressive disorder |
| Sleep | Snoring, witnessed apneas, daytime sleepiness, obesity | Obstructive sleep apnea |
| Chronic, after exclusion | Six months or more, worse after exertion, unrefreshing sleep | ME/CFS |
Clinical notes
- Fatigue with weight loss, fever, night sweats or lymphadenopathy: look for tuberculosis, HIV, lymphoma or another cancer.
- Objective weakness, drooping eyelids or double vision worse at the end of the day suggest a neuromuscular disease rather than fatigue.
- Fatigue with low blood pressure, vomiting and abdominal pain may be an adrenal crisis.
- Thoughts of self-harm or suicide need same-day assessment.
- In older adults, fatigue may be the presenting symptom of heart failure, infection, depression or medicine side effects.
In the lab
- Complete blood count and ferritin.
- Thyroid-stimulating hormone, glucose or HbA1c, electrolytes, creatinine and liver tests.
- Pregnancy test when relevant; inflammatory markers, HIV and other tests guided by the history.
- Sleep study when sleep apnea is suspected.
Test yourself
Think of the answer, then tap the question to see it.
How is fatigue distinguished from sleepiness?
Sleepiness is a tendency to doze off that improves with sleep; fatigue is a lack of energy that rest does not fully relieve.
From what duration is fatigue called chronic?
Six months or more.
Which pattern of fatigue through the day suggests depression?
Worse in the morning and improving as the day goes on, often with early waking and loss of interest.
Which are the red flags in a patient with fatigue?
Weight loss, fever or night sweats, lymphadenopathy, objective weakness, bleeding, dyspnea or chest pain, or thoughts of self-harm.
Connections
See it in 3D1
The structures of Durgical's 3D anatomy where it is found.
Educational content on the clinical exam; it is learned and practised under supervision. It does not replace assessment by a health professional and is not for self-diagnosis.
Sources: Fatigue (MedlinePlus Medical Encyclopedia, U.S. National Library of Medicine, 2025); Fatigue in Adults: Evaluation and Management (American Family Physician (American Academy of Family Physicians), 2023).
Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake
Representative model, for educational purposes only.