What does Synthroid do for your body?

Synthroid (levothyroxine) is a synthetic (human-made) version of thyroxine (T4), a hormone naturally produced by the thyroid gland. It works by replacing or supplementing the thyroid hormone that your body is missing when you have hypothyroidism. Thyroid hormones are involved in regulating many processes in the body, including metabolism, growth, body temperature, and heart rate. View original source