Unexplained weight loss occurs when people lose weight without changing their diet or exercise routine. Possible causes include thyroid problems, depression, inflammatory bowel disease (IBD), and cancer.

Most people are very aware of the dangerous consequences of weight gain, and many articles focus on ways to lose weight. However, unintended weight loss can also jeopardize a person’s health or indicate an underlying medical condition.

People may gain or lose weight in response to seasonal changes or when facing important or stressful life changes, such as moving home or starting a new job.

However, a person may wish to see a doctor if they experience significant weight loss that has no clear explanation.

In this article, learn about the possible causes of unexplained weight loss and when to see a doctor.

A woman researches what causes unexpected weight lossShare on Pinterest
Getty Images

Several medical conditions can cause unexplained weight loss. People can help their doctor pinpoint the underlying cause by paying attention to any additional symptoms that they experience.

The following problems and conditions may cause unexplained weight loss:


Hyperthyroidism occurs when the thyroid gland produces more hormones than the body requires. People sometimes refer to this condition as an overactive thyroid.

The thyroid produces certain hormones that regulate the body’s metabolism, so an excess of these hormones often causes the body to burn more energy than usual. Burning more energy and calories can lead to unintentional or unexplained weight loss.

Other symptoms of hyperthyroidism include:


The symptoms of depression can also cause weight loss.

In a 2017 prospective study, researchers examined the causes of unexplained weight loss in 2,677 adults. They identified depression as the underlying cause in 7% of the participants.

According to the researchers behind a 2016 study, there is evidence to suggest that people with depression may have associated suppressed interplay among the hypothalamus, pituitary gland, and adrenal glands, which may affect the function of the gastrointestinal (GI) tract.

Changes to the hypothalamus and pituitary gland can also affect the adrenal glands, which produce multiple hormones. These hormones include cortisol, which helps regulate blood pressure, blood glucose level, and metabolism.

Other symptoms of depression include:

  • persistent or recurring feelings of sadness, hopelessness, or apathy
  • changes in appetite, such as eating more or less than usual
  • unintentional weight loss or weight gain

Addison’s disease

Addison’s disease is most commonly due to a rare autoimmune disease that harms the adrenal glands and prevents them from producing enough cortisol and aldosterone.

People who have Addison’s disease might notice a decrease in their appetite as well as unexplained weight loss, according to the National Institutes of Health (NIH).

Other symptoms of Addison’s disease include:

Inflammatory bowel disease

Inflammatory bowel disease (IBD) refers to two inflammatory gastrointestinal conditions with immune system dysfunction: Crohn’s disease and ulcerative colitis.

Crohn’s disease can cause inflammation in any part of the gastrointestinal tract, from the mouth to the anus. Ulcerative colitis, on the other hand, only affects the large intestine.

IBD can reduce the body’s ability to digest food properly or absorb nutrients, which can lead to malnutrition.

Weight loss is a common symptom of both conditions, especially among younger people. Other symptoms of IBD include:

  • frequent diarrhea
  • abdominal pain
  • bloody stools due to GI tract bleeding
  • fatigue
  • fever

Muscle loss

Muscle loss, also known as muscle atrophy, occurs when the muscles shrink or waste away. This condition can cause unexplained weight loss.

Possible causes of muscle loss include:

People can often prevent muscle loss through proper nutrition and regular exercise. Physical therapy after an injury or stroke may help reverse or prevent muscle loss.

Rheumatoid arthritis

Rheumatoid arthritis (RA) is an autoimmune disorder that causes inflammation in the joints.

Although the Arthritis Foundation estimate that two-thirds of people who have RA are overweight or have obesity, people who have RA may experience weight loss.

This weight loss may occur because the chronic inflammation that RA causes forces the body to use more energy. In addition, people who have RA may experience muscle loss because the inflammation in their joints keeps them from engaging in regular physical activity.

Some medications that people take to treat RA may cause side effects, such as diarrhea and loss of appetite, which can also contribute to weight loss.


Although cancer symptoms tend to vary depending on the type, stage, and location of the disease, unexplained weight loss is sometimes a sign of cancer.

Cancer refers to any disease in which abnormal and mutated cells rapidly multiply and eventually invade healthy tissue.

Weight loss is especially common in lung cancer and cancers that affect the digestive tract, such as:

Other early symptoms of cancer to pay attention to include:

  • fatigue
  • fever
  • pain
  • digestive issues
  • changes in bowel or bladder function
  • skin changes
  • a persistent cough

Other possible causes

A person may also experience unexplained weight loss as a result of:

Anyone can experience unexplained weight loss, regardless of their sex. However, whether a person is male or female can increase their risk for certain conditions that can cause this symptom.

According to a 2018 study, adult women who are between the ages of 25–29 years or older than 35 years have a significantly higher risk than men of Crohn’s disease. After 45 years of age, men have a substantially higher risk of ulcerative colitis than women.

Compared with men, women are also much more likely to develop hyperthyroidism and RA.

According to the Centers for Disease Control and Prevention (CDC), depression affected almost twice as many women as men between 2013 and 2016.

However, the American Cancer Society state that men have a higher risk of developing stomach cancer. Men are also at higher risk than women for developing pancreatic cancer.

While body weight can fluctuate naturally, a person should contact a doctor if they lose more than 5% of their baseline body weight within 6–12 months without making any changes to their diet or exercise routine.

A doctor may be able to diagnose the underlying cause of unexplained weight loss by performing a physical examination and reviewing a person’s medical history.

They may also use blood tests, including hormone panels, or imaging studies to rule out specific medical conditions, such as hypothyroidism, RA, or cancer.

Unexplained weight loss has many potential underlying causes, which range from inflammatory conditions to psychological disorders.

People can help their doctor identify the exact cause by recording any additional symptoms that they are having.