Sudden weight loss may be caused by anorexia nervosa, hyperthyroidism, tuberculosis, etc. The specific reasons need to be examined in the hospital to determine. 1. Anorexia nervosa: Anorexia nervosa is generally related to biological, psychological and environmental factors. Patients may suffer from sudden weight loss due to excessive dieting or refusal of food, and some of them may also take appetite suppressants, excessive exercise and diarrhea to reduce their weight, and they may suffer from symptoms such as anxiety, extreme thinness, and abnormal behavior. 2. Hyperthyroidism: Hyperthyroidism is usually caused by heredity, autoimmune diseases, long-term mental stimulation, etc. Patients will experience significant weight loss, even if the patient’s meal intake is not reduced or increased compared to the previous, the patient will also experience excessive sweating, hyperphagia, and persistent rapid heartbeat and other symptoms. 3. Tuberculosis: Tuberculosis is mostly caused by living in crowded places for a long time, poor nutrition, weak immune system, etc. The main symptoms of patients are coughing, coughing up sputum, and some of the patients will also have systemic symptoms, such as loss of appetite, weight loss, night sweats, and intermittent or persistent afternoon low-grade fever. There are many reasons for sudden weight loss, so if you have symptoms, you can observe them for a while, and if they are accompanied by other symptoms, you should go to the hospital in time and follow the doctor’s instructions.