Always tired – the causes worth testing for
Persistent exhaustion is one of the commonest reasons people see a doctor, and several of the causes are simple blood tests away.
Tired versus exhausted
Being tired after a hard week is ordinary. What is worth investigating is fatigue that does not lift with rest, that has lasted weeks, or that is out of proportion to what you are doing — particularly with any other symptom alongside it.
It is easy to attribute this to stress or age and leave it, and several of the actual causes are both common and straightforwardly treatable.
The causes worth excluding
- Anaemia, most often iron deficiency. Very common in South African women, and a simple blood test.
- An underactive thyroid — tiredness, weight gain, feeling cold, dry skin, constipation.
- Diabetes — tiredness with thirst, passing a lot of urine, blurred vision.
- Depression, which very often presents as physical exhaustion rather than sadness.
- Sleep apnoea — loud snoring, pauses in breathing, waking unrefreshed, daytime sleepiness.
- HIV, which can cause fatigue long before anything else. Testing is free and quick.
- TB, particularly with night sweats, weight loss or a cough over two weeks.
- Chronic kidney disease, heart failure, and some cancers.
- Medication — blood pressure tablets, antihistamines, some antidepressants.
- Vitamin B12 or vitamin D deficiency.
The things that are not tests
- Sleep: enough hours, a consistent time, and a look at whether snoring is disrupting it.
- Alcohol, which fragments sleep even when it helps you fall asleep.
- Caffeine late in the day.
- Physical activity — counterintuitively, being more active reduces fatigue rather than adding to it.
- Eating regularly and enough. Skipping meals is a common and overlooked cause.
- Stress and load. Fatigue is a reasonable response to an unreasonable amount, and no test will show it.
When to go sooner
Common questions
- Should I just take a multivitamin or an iron supplement?
- Not blindly. Taking iron without a confirmed deficiency causes constipation and can be harmful in some conditions, and it can mask a cause that needed finding — iron deficiency in an adult sometimes signals bleeding that needs investigating. Get tested first.
- Could it be a vitamin B12 deficiency?
- It can, particularly in vegetarians and vegans, older adults, people on long-term metformin or acid-suppressing medicines, and after some gut surgery. It is a blood test worth asking about if you fit any of those.
- How long should I wait before seeing someone?
- If fatigue has persisted for more than a few weeks without an obvious explanation, or comes with any of the warning signs above, go now rather than waiting for it to lift on its own.
Sources
- Primary Healthcare Standard Treatment Guidelines and Essential Medicines ListNational Department of Health, South Africa
- Communicable disease surveillance and clinical guidanceNational Institute for Communicable Diseases, South Africa
Last reviewed 4 August 2026.