Hormone therapy: Treatment of disease or symptoms with synthetic or naturally derived hormones. The term is most commonly used to describe use of medications containing both estrogen and progestogen to reduce or stop short-term changes associated with the perimenopause. In the more general sense, hormone therapy may be used to treat some forms of cancer, taking advantage of the fact that certain cancers depend on hormones to grow. It may also be used for thyroid disorders, and illnesses associated with hormone production or use. Hormone therapy may include giving hormones to the patient or using medications that decrease the level of hormones in the body.