Tamoxifen is a tablet taken by mouth and is a type of hormone therapy called an anti-estrogen. Some forms of cancer grow and respond to the presence of the hormone estrogen in the body. Tamoxifen acts to block the estrogen receptors on these cancers, and causes the cancer cells to stop growing and die.

Tamoxifen is also sold under the trade names Nolvadex, Istubal, and Valodex.