Sudden, noticeable weight loss can happen after a stressful event, although it can also be a sign of a serious illness.

It's normal to lose a noticeable amount of weight after the stress of changing jobs, divorce, redundancy or bereavement. Weight often returns to normal when you start to feel happier, after you've had time to grieve or get used to the change. Counselling and support may be needed to help you get to this stage.

Significant weight loss can also be the result of an eating disorder, such as anorexia or bulimia. If you think you have an eating disorder, talk to someone you trust and consider speaking to your GP. There are also several organisations you can talk to for information and advice, such as the eating disorders charity Beat.

If your weight loss wasn't a result of the above causes, and you didn't lose weight through dieting or exercising, see your GP as you may have an illness that needs treating.

The following information may give you a better idea of the cause of your weight loss, but don't use it to diagnose yourself. Always see a GP for a proper diagnosis.

Other common causes of unexpected weight loss

Unintentional weight loss doesn't always have an identifiable underlying cause but, in addition to the causes mentioned above, it's often the result of:

• depression 
• an overactive thyroid gland (hyperthyroidism), or over-treating an underactive thyroid
• cancer

Less common causes of unexpected weight loss

Less frequently, unexpected weight loss may be the result of:

• the side effects of certain medications
• alcohol misuse or drug misuse 
• heart, kidney, lung or liver disease
• a problem with the glands that secrete hormones, such as Addison's disease or undiagnosed diabetes
• a long-term inflammatory condition, such as rheumatoid arthritis or lupus
• a disease of the gut, such as a stomach ulcer, inflammatory bowel disease (IBD) or coeliac disease
• a bacterial, viral or parasitic infection, such as persistent gastroenteritis, tuberculosis (TB) or HIV and AIDS

Click on the links above for more information about these causes, including advice on how to manage them.