What is the most common cause of unexplained weight loss?

Weight may fall when you eat less, absorb fewer nutrients, or use more energy than usual. Depression can reduce appetite and make shopping or preparing meals difficult. Hyperthyroidism can speed body processes and may occur with heat intolerance, tremor, sweating, or a racing heartbeat. Type 1 diabetes may cause thirst and frequent urination, while type 2 diabetes can also affect weight and energy. Coeliac disease and Crohn's disease may interfere with digestion or absorption. The same symptom has many possible explanations, so weight loss does not identify a specific disease by itself.

Arrange a medical appointment if weight is falling without a planned change in diet or activity. Before the visit, note your usual appetite, meals, bowel pattern, thirst, urination, mood, sleep, and any swallowing difficulty. Bring a list of medicines and supplements. Continue nourishing meals and fluids if you can, but avoid trying to correct ongoing loss with supplements alone before the cause is assessed.

Seek prompt care for severe weakness, confusion, inability to keep fluids down, fainting, difficulty swallowing, blood in stool, or new marked thirst with frequent urination. Contact a clinician soon for continuing loss, night sweats, persistent fever, ongoing diarrhoea, breathing symptoms, or a major change in mood. These features help determine how quickly you need examination and testing.

Ask what examinations or blood tests may clarify the cause, whether your medicines could affect appetite or digestion, and what amount of further loss should trigger an earlier review. Share the timing and pace of the change rather than relying on memory.