Mistletoe, or Viscum album is a semi-parasitic plant that grows on oaks and other trees in Europe and Asia. Mistletoe is also found in America and Korea, but normally only the European species is used in the treatment of cancer, inflammatory conditions and AIDS. The leaves, twigs, and berries are what is used to make these herbal medicines.

Because the medicinal doses are small (it can be poisonous in large doses), many believe it to be "homeopathic," but it isn't.

Mistletoe was first proposed for the treatment of cancer in 1920 by Rudolph Steiner, an Austrian Swiss physician who founded the Society for Cancer Research to promote mistletoe extracts and anthroposophical medicine.

Mistletoe extracts are marketed under several trade names, such as Iscador, Helixor, Eurixor, and Isorel, most of which are available in Europe. Weleda AG manufactures Iscador, which consists of fermented extracts of mistletoe, sometimes combined with trace amounts of silver, copper or mercury.