Unintentional weight loss is when you lose weight without changing your diet or exercise routine — and it can have many different causes. ^1,3

It is important to get checked if you are losing weight without trying, as it can sometimes be a sign of an underlying health condition.¹

Understanding Unintentional Weight Loss?

Your body weight can regularly go up and down, and this is normal. However, the persistent, unintentional loss of more than 5% of your body weight over 6 to 12 months is usually a cause for concern.¹

Why should unintentional weight loss not be ignored?

Your weight is a critical piece of your health puzzle; it can signal a problem or be the cause of health issues. If your weight unexpectedly drops without a reason, you may have an underlying health problem.²

Common Causes of Unintentional Weight Loss

Unintentional weight loss can have many different causes which can be grouped into ^3,4

Medical conditions

• Hormone conditions such as overactive thyroid or diabetes.
• Digestive disorders such as coeliac disease or inflammatory bowel disease.
• Chronic infections such as tuberculosis or HIV.
• Heart, kidney, or lung disease; including heart failure, chronic kidney disease, and chronic obstructive pulmonary disease.
• Neurological conditions such as Parkinson’s disease, stroke, or dementia.
• Dental problems such as losing teeth, having new orthodontics or mouth ulcers
• Cancer

Psychological causes

• Depression and anxiety
• Eating disorders
• Stress, obsessive-compulsive disorder, or schizophrenia
• Memory loss

Lifestyle and social causes

• Poor nutrition or lack of appetite
• Financial difficulty or problems accessing food³

Can Medications Cause Weight Loss?

Yes. A range of medicines can cause unintentional weight loss as a side effect. These include cardiac, neurologic and psychiatric diseases, and tablets used for treatment of diabetes mellitus and pain management.⁵

What Are the Symptoms of Unintentional Weight Loss?

Symptoms linked to unintentional weight loss can include tiredness, loss of appetite, a change in your toilet habits and an increase in illnesses or infection.¹

When Should You See a doctor?

If you keep losing weight without changing your diet or exercise routine

It’s important to see a GP as soon as possible if you have weight loss and other symptoms. The earlier the cause is found, the sooner it can be treated.

How Doctors Diagnose the Cause of Unintentional Weight Loss?

1. Your HCP will ask for a detailed history and run a clinical examination which are necessary to guide appropriate investigations to determine the cause of unintentional weight loss.⁶

1. Your HCP might ask you to fill in specific questionnaires to screen some individual conditions.⁶

1. You might need to carry out some diagnostic investigations including simple blood tests and radiological imaging such as a chest X‑ray.⁶

Unintentional weight loss is a common symptom, particularly among older patients.

The differential diagnosis of the underlying diseases leading to unintentional weight loss includes both malignant and nonmalignant gastrointestinal diseases, as well as endocrine, infectious, cardiopulmonary, and psychiatric disorders and side effects of medications.

The diagnostic approach to unintentional weight loss includes medical history, physical examination, laboratory testing, imaging, and endoscopy. It’s important to get checked if you’re losing weight without trying.

Key takeaways

• Unexpected weight loss is your body’s way of signaling that something may be wrong.²
• A loss of more than 5% of body weight over 6–12 months without trying warrants medical evaluation. ¹
• Your healthcare provider can usually identify the cause through your medical history, physical examination, and appropriate tests. ⁶

References

1. nidirect (2017) Unintentional weight loss. nidirect Government Services. Available at: https://www.nidirect.gov.uk/conditions/unintentional-weight-loss (Accessed: 14 May 2026).
2. UCLA Health (2024) Unexplained weight loss: What it could mean. Available at: https://www.uclahealth.org/news/article/unexplained-weight-loss-what-it-could-mean (Accessed: 14 May 2026).
3. NHS (2025) Unintentional weight loss. National Health Service. Available at: https://www.nhs.uk/symptoms/unintentional-weight-loss/ (Accessed: 14 May 2026).
4. Stajkovic, S., Aitken, E.M. and Holroyd-Leduc, J. (2011) Unintentional weight loss in older adults. CMAJ: Canadian Medical Association Journal, 183(4), pp. 443–449.
5. Abu Freha, N. (2018) Unintentional Weight Loss. In: Weight Loss. Rijeka, Croatia: IntechOpen. Available at: https://doi.org/10.5772/intechopen.74860 (Accessed: 14 May 2026).
6. Soo, M.R.T., Khor, J.H., Cheah, M.H. and Nashi, N.B. (2024) Approach to weight loss in adults. Singapore Medical Journal, 65(5), pp. 291–294.
7. Inadomi, J.M., Bhattacharya, R., Hwang, J.H. and Ko, C. (2019) The Patient with Unexplained Weight Loss. In Yamada’s Handbook of Gastroenterology. Wiley-Blackwell.