About this symptom
Unexplained weight loss means losing weight without trying, through dieting or exercise. Doctors become concerned when someone loses about 4.5 kg, or 5 per cent of their usual weight, over 6 to 12 months or less with no known reason.
It can be a sign of many different things, from low mood and stress to long-term infections, hormone problems and cancer. Cancer can cause weight loss even when there are no other symptoms, so the cause should always be looked for.
Possible causes
This is not a diagnosis. These are the causes doctors think about, with the ones that are most urgent to rule out first.
- CancerSome cancers cause weight loss even before any other symptom appears, which is why unexplained weight loss always needs checking.
- TuberculosisWeight loss with a cough that lasts more than 3 weeks, fever or night sweats, constant tiredness and poor appetite.Read about it
- Type 2 diabetesWeight loss with constant thirst, passing urine more often and feeling very tired. A blood test finds it.Read about it
- Overactive thyroidWeight loss with sensitivity to heat and a fast or irregular heartbeat. A blood test checks thyroid function.Read about it
- Stomach ulcerIndigestion or tummy pain that keeps coming back, poor appetite, feeling full after very little food, or trouble swallowing.Read about it
- DepressionLow mood, worry or stress can reduce appetite. Tell the doctor how you have been feeling.Read about it
- Poor absorption of foodLong-lasting diarrhoea or a gut problem such as coeliac disease can stop the body taking enough from food.
When to get help
See a doctor soon for:
- Losing about 4.5 kg, or 5 per cent of your weight, over 6 to 12 months or less without trying
- Weight loss with fever, night sweats or constant tiredness
- Weight loss with a cough that has lasted more than 3 weeks
- Weight loss with constant thirst and passing urine more often
- Weight loss with indigestion, poor appetite, feeling full after very little food, or trouble swallowing
- Weight loss with sensitivity to heat, or a fast or irregular heartbeat
Even without these signs, losing weight for no clear reason is a reason to book a visit. Weight lost on purpose, by eating less or exercising more, is not a worry.
What you can do at home
There is no home treatment for unexplained weight loss, because the cause has to be found first. With any emergency sign, do not stay at home.
Do
- Note when the weight loss began, how much you have lost and how fast
- Write down other changes: appetite, thirst, cough, fever, sweats, bowel habits, tiredness and mood
- Bring a list of every medicine you take
Do not
- Do not put it off because you feel well
- Do not try to fix it with tonics or supplements before the cause is known, as the right diet advice depends on the cause
- Do not stop or change a medicine yourself, even if you think it is the cause
What the doctor will do
The doctor will weigh you and examine you. They will ask how much weight you have lost, how fast and when it began, about your eating and exercise, recent illnesses, mouth or teeth problems, stress and mood, vomiting, fainting, hunger, thirst, passing urine, bowel habits and your medicines.
Tests depend on the likely cause. They may include blood tests, such as blood sugar and thyroid function, and a chest X-ray or other scans. If TB is suspected, samples of phlegm are tested too. Some people are referred to a dietitian for advice on food.
Myths and facts
Things people often say about this. Open each one to see what is true.
Myth“Losing weight is always good, so there is nothing to check.”What is true?
Fact
Weight lost without trying is a warning sign, not an achievement. It can come from diabetes, an overactive thyroid, TB, low mood or cancer, and finding the cause early makes treatment easier.
Myth“If there is no pain and I feel well, it cannot be anything serious.”What is true?
Fact
Cancer can cause weight loss even when there are no other symptoms. Feeling well is not a reason to wait, so have unexplained weight loss checked.
Myth“It is only stress, and it will settle by itself.”What is true?
Fact
Stress and low mood can reduce appetite, but they are not the only cause, and a doctor needs to rule out the others. If stress is the cause, that can be helped too.
Questions to ask your doctor
Tick the ones you want answered and take them with you.
Common questions
How much weight loss counts as unexplained weight loss?
Doctors usually take notice when someone loses about 4.5 kg, or 5 per cent of their usual weight, over 6 to 12 months or less without trying and without a known reason. Losing more weight than is healthy for your age and height is also a reason to be checked.
Can stress make me lose weight?
Yes. Low mood, worry and stress can reduce appetite and lead to weight loss. But other causes need to be ruled out, so do not assume. Tell the doctor how you have been feeling as well as what you have noticed in your body.
Should I be worried about cancer?
Weight loss has many possible causes, including diabetes, an overactive thyroid, TB, stomach problems and low mood. Cancer is one of them, and it can cause weight loss even without other symptoms. That is why the cause should be looked for rather than guessed.
How can I prepare for the appointment?
Note when the weight loss started and how much you have lost. Write down any other changes, such as appetite, thirst, cough, fever, sweats, bowel habits and mood, and bring a list of your medicines.
