A high thyroid T4 is one of the indicators of the body’s thyroid function. A high thyroid T4 means that hyperthyroidism may occur. There are many reasons for high T4 in the body due to hyperthyroidism. First of all, high thyroid T4 may be caused by genetic factors. The likelihood of hyperthyroidism is higher in offspring with a family history of hyperthyroidism, and high thyroid T4 is one of its common indicators. In addition, high thyroid hormones may also be caused by geographical factors. The lack of iodine in inland areas far from the sea often causes thyroid disorders in humans, resulting in hyperthyroidism and high thyroid T4. Once high thyroid hormones are detected, reasonable treatment measures should be taken to avoid adverse complications.