Causes of involuntary weight loss include depression, chronic illness, infections, stress and anxiety. Certain drugs, such as chemotherapy and thyroid medications, and drug abuse are also causes of weight loss, according to MedlinePlus.
Weight loss occurs when a person starts losing weight without any changes in diet or physical activity. It could indicate something minor or something more severe. Cancer, hyperthyroidism, abdominal infections, gastroenteritis and celiac disease are causes of unintentional weight loss. Dementia, malnutrition and HIV are also causes, explains Healthline.
Medical attention is recommended if a person has lost over 10 pounds or five percent of his body weight within six months to a year for an unknown reason. Medical attention is also required if there are symptoms related to the weight loss, states MedlinePlus.