Unexplained weight loss has many causes, medical and nonmedical. Often, a combination of things results in a general decline in your health and a related weight loss. Most often, medical disorders that cause weight loss include other symptoms. Sometimes a specific cause isn't found.

Potential causes of unexplained weight loss include

• Cancer
• Dementia
• Dental problems
• Depression (major depressive disorder) or other mood disorders
• Diabetes
• Hypercalcemia (high blood calcium level)
• Hyperthyroidism (overactive thyroid)
• Hyponatremia (low blood sodium level)
• Medicines
• Parkinson's disease
• Previous stroke or neurological disorders

Less common conditions that may include weight loss as one of the symptoms are:

• Addison's disease (adrenal insufficiency)
• Alcohol use disorder
• Amyloidosis (buildup of abnormal proteins in your organs)
• Celiac disease
• COPD (chronic obstructive pulmonary disease) — the blanket term for a group of diseases that block airflow from the lungs — including emphysema.
• Crohn's disease
• Drug addiction (substance use disorder)
• Heart failure
• HIV/AIDS
• Peptic ulcer
• Prescription drug abuse
• Tuberculosis
• Ulcerative colitis (a type of inflammatory bowel disease)

Unexplained weight loss, or losing weight without trying — particularly if it's significant or ongoing — may be a sign of a medical disorder.

The point at which unexplained weight loss becomes a medical concern is not exact. But many health care providers agree that a medical evaluation is called for if you lose more than 5% of your weight in 6 to 12 months, especially if you're an older adult. For example, a 5% weight loss in someone who is 160 pounds (72 kilograms) is 8 pounds (3.6 kilograms). In someone who is 200 pounds (90 kilograms), it's 10 pounds (4.5 kilograms).

Your weight is affected by your calorie intake, activity level and overall health. Your ability to absorb nutrients from the food you eat also affects your weight. Economic and social factors also may play a role.

If you're losing weight without trying and you're concerned about it, consult your health care provider. As a rule of thumb, losing more than 5% of your weight over 6 to 12 months may indicate a problem. If you're an older adult with other medical conditions and health issues, even a smaller amount of weight loss may be significant.

Your health care provider can work with you to try to determine what's causing the weight loss. You'll likely start with a thorough discussion of your symptoms, medications, general mental and physical health, and medical conditions. Also, your provider will probably do a physical exam.

Your health care provider also will likely review any recent cancer screenings you may have had. These can include a colon cancer screening test, breast exam and mammogram, or a prostate exam. This can help determine if additional testing is needed.

Your provider may also discuss changes in your diet or appetite and sense of taste and smell. These can affect your eating and weight and may be related to some medical conditions.

Your health care provider may order blood and urine tests that can give information about your general health. You may have other tests based on these results. Imaging scans to look for hidden cancers are not usually done unless some other clue in addition to weight loss points in that direction.

Sometimes, if the basic evaluation does not identify a cause, watchful waiting for 1 to 6 months is a reasonable next step. Your health care provider may suggest that you stop any restrictive dieting. You may need a special diet to prevent further weight loss or to regain lost pounds. Your provider can refer you to a dietitian who can offer suggestions on getting enough calories.