'Tis the season for hanging mistletoe, a tradition that originated in Roman times for celebrations of Saturnalia -- a mid-winter festival honoring Saturn, the god of agriculture. If you did not realize that your annual holiday decorations reflected a centuries-old practice, you may be even more surprised to learn that mistletoe also played a role in traditional medicine and complementary therapies. These therapies were used to treat a myriad of health issues, including seizures, tumors, hypertension, headaches, gynecological complaints, and the list goes on!
Mistletoe grows all over the world. There are over 1,000 species, all of which are poisonous to humans. The most common species native to the Americas, Phoradendron leucarpum, does not seem to have any therapeutic value. However, its European cousin, Viscum album (also known as European mistletoe), appears as an ingredient for therapeutic remedies in several classic works.
Hippocrates (460-370 BC) included mistletoe in treatments for spleen disorders and menstrual complaints. In De Medicina, Aulus Cornelius Celsus (25 BC-50 AD) detailed his use of mistletoe to reduce scrofulous tumors -- a type of swelling in the neck caused by bacterial infection of the lymph nodes. Pedanius Dioscorides (40-90 AD) included mistletoe in his great herbal treatise De Materia Medica as a treatment for conditions such as epilepsy. His contemporary, Pliny the Elder (23-79 AD), described in De Naturalis Historia how the Druids revered mistletoe growing on oak trees as a sacred plant. They claimed its juice could render barren animals fertile and serve as an antidote for any poison -- an interesting claim for a poisonous plant.
In 1719, English physician John Colbatch published the first edition of his Dissertation Concerning Misletoe: a Most Wonderful Specifick Remedy for the Cure of Convulsive Distempers. Colbatch expressed interest in developing a treatment after noting that fatalities in children suffering from convulsions or seizures accounted for one-fifth of deaths reported in the London Bills of Mortality. He recalled the Druids' use of mistletoe and decided to experiment. Colbatch was disappointed that he couldn't find much mistletoe growing on nearby oak trees, but he found plenty on the local English lime trees, also known as linden trees. He ground the European mistletoe into a powder, which he made into an oral solution and administered a few droplets at a time to his patients. He reported that it reduced the heart rate, calmed fits, and prolonged intervals between fits. Colbatch's reported success in using mistletoe as an anti-convulsive treatment in children sparked widespread interest. An expanded second edition appeared in 1720. By 1730, a total of 6 editions were published. NLM holds all 6 editions in its collection, plus a 1776 German edition.
In 1916, controversial Austrian philosopher Rudolf Steiner (1861-1925) proposed the idea of using mistletoe extract to cure cancer. A year later, Dutch physician Ita Wegman produced a diluted extract for intravenous injection. Steiner and Wegman co-founded the Anthroposophic Medicine movement -- a form of holistic medicine that emphasizes treating mind, body, and soul. Similar to homeopaths, anthroposophists believed in the principle of "like cures like." Since parasitic mistletoe eventually kills its host plant, they reasoned, mistletoe extract should in turn kill cancer cells. Wegman's mistletoe extract was marketed by homeopathic drug stores under the name Iscador and it remains a part of the homeopathic pharmacopeia today.
In recent decades, there have been numerous clinical trials of this approach in Europe, and mistletoe extract has been approved for use in Germany as a cancer therapy. Proponents insist it improves cancer patient quality of life and prolongs life expectancy. However, skeptics criticize the research models of the European clinical trials and claim that the results are inconclusive. In 2023, researchers at the Johns Hopkins Kimmel Cancer Center launched a Phase I clinical trial of intravenous mistletoe extract (Helixor M) as a therapy for advanced cancer patients. It was the first clinical trial of mistletoe extract in the United States. The study aimed to determine safety parameters and dosing guidelines to help inform a future Phase II trial. The research results were published in Cancer Research Communications in February 2024.