Antiestrogen

An antiestrogen is a substance that blocks the production or utilization of estrogens, or inhibits their effects. Estrogens are the family of hormones that promote the development and maintenance of female sex characteristics.

Although aromatase inhibitors could be considered antiestrogens by some definitions, they are often considered to be a distinct class. Aromatase inhibitors reduce the production of estrogen, while the term "antiestrogen" is usually reserved for agents reducing the response to estrogen.