The main causes of low thyroid stimulating hormone are subclinical hyperthyroidism, hyperthyroidism and pituitary diseases. Different causes have different symptoms, mainly involving the cardiovascular system, eyes, gastrointestinal system, neuropsychiatric system, endocrine system and other symptoms. 1. Hyperthyroidism: tachycardia, atrial fibrillation, panic, shortness of breath, protruding eyes, excessive food and hunger, nausea, vomiting, abdominal pain, increased frequency of bowel movements, irritability, hair loss, menstrual disorders and infertility. 2. Subclinical hyperthyroidism: low levels of thyroid stimulating hormone, but thyroid hormone levels are in the normal range, often without obvious clinical symptoms. 3. Pituitary diseases: for example, pituitary tumor, pituitary inflammation, etc., which will show low metabolic symptoms, such as bradycardia, chills, edema, drowsiness, memory loss, and indifference. When low thyroid stimulating hormone occurs, it is recommended to seek medical treatment in time and under the guidance of the doctor.