Hormones are special chemicals released by glands in the body to control virtually all bodily processes. They act like messengers telling the different organs and parts of the body how to react or what to do. Imbalances in hormone levels caused by a hormone deficiency can lead to many different symptoms and medical conditions. Replacing the body's natural hormones can effectively manage these conditions. For example, people with underactive thyroid gland (hypothyroidism) can take levothyroxine to replace their thyroid hormone. Replacing oestrogen and progestogen (a treatment known as HRT) can relieve menopausal symptoms and reduce the risk of osteoporosis. Corticosteroids (or oral steroids) such as fludrocortisone and hydrocortisone are given to replace hormones normally produced by the adrenal glands.