Viscum album. Mistletoe preparations have been used medicinally in Europe for centuries to treat epilepsy, infertility, hypertension, and arthritis. The Celtic priests, known as Druids, revered the oak tree and the mistletoe that grew on it, according to Roman author and naturalist Gaius Plinius Secundus (also known as Pliny the Elder). At the winter celebration of Samhain, the sacred oaks were bare except for the green boughs of mistletoe, and this was taken as a sign of eternal fertility. The Celts placed a sprig of mistletoe above the door of their houses and its sacred nature prohibited fighting beneath it. This evolved over centuries into the custom of kissing underneath mistletoe at Christmas. In 1921, the Austrian anthroposophical spiritual leader Rudolf Steiner suggested that mistletoe might be used to treat cancer, based on the observation that mistletoe, like cancer, is parasitic and lethal to its host. Swiss and German clinics were founded to implement this idea and still actively use a mistletoe preparation fermented with a strain of Lactobacillus for 3 days. Mistletoe extracts contain several toxic proteins, several of which are lectins, or proteins capable of binding to specific sugars.Mistletoe has been used to treat cancer, although there is a lack of quality clinical trials and no evidence of an effect. Most evidence is ancedotal and based on case reports. Further study is needed. In folk medicine, it has been used for its cardiovascular properties, but its clinical efficacy has not been established. Injectable mistletoe extract is widely used in Europe but is not licensed for use in the United States.