Mistletoe has been used medicinally for over 2,000 years, treating everything from seizures to headaches. Today its most significant use is in cancer care, where European mistletoe extract is one of the most commonly prescribed complementary therapies for cancer patients in countries like Germany, Austria, and Switzerland. It also remains a familiar holiday decoration, particularly in the United States, where it holds more cultural significance than medicinal.
Two Different Plants, Two Different Traditions
The word “mistletoe” actually refers to two unrelated species. European mistletoe (Viscum album) is a parasitic vine found across Europe, Northern Africa, and Southern Asia. American mistletoe (Phoradendron leucarpum) is native to North America. Both are semi-parasitic, growing on the branches of host trees and drawing water and nutrients from them.
European mistletoe is the one with a long medicinal history and active clinical use. American mistletoe is known primarily as a Christmas decoration, though extracts were historically used to treat low blood pressure. When you see mistletoe discussed in a medical context, it almost always refers to the European species.
Historical Medicinal Uses
Mistletoe has been part of herbal medicine since antiquity. The Greek physician Dioscorides, writing around 70 AD, included it in his foundational herbal text as a treatment for epilepsy. Centuries later, in 1719, the English physician John Colbatch published a dissertation calling mistletoe “a most wonderful specifick remedy for the cure of convulsive distempers.” He reported that it reduced heart rate, calmed fits, and lengthened the intervals between episodes.
Over the centuries, practitioners used mistletoe preparations for seizures, tumors, high blood pressure, headaches, and various gynecological complaints. Much of this was observational rather than scientifically tested, but it laid the groundwork for modern interest in the plant.
Mistletoe in Cancer Care
The modern use of mistletoe in oncology traces back to 1920, when Rudolf Steiner, the founder of anthroposophic medicine, first proposed mistletoe extracts as a cancer treatment. A century later, these extracts are among the most frequently prescribed complementary drugs for cancer patients in parts of Europe. They’re typically given as injections under the skin.
Clinical trials have studied mistletoe extracts across a wide range of cancers: breast, lung, ovarian, uterine, colorectal, pancreatic, stomach, bladder, head and neck cancers, melanoma, and bone cancer. The primary goals of these studies have been improving quality of life, managing symptoms like fatigue, nausea, and pain, and evaluating whether the extracts affect survival.
A systematic review and meta-analysis covering 26 publications found a statistically significant, medium-sized improvement in overall quality of life for cancer patients receiving mistletoe extracts compared to controls. Half of the specific quality-of-life categories measured, including pain and nausea, showed significant improvement. The benefit was stronger in younger patients and with longer treatment durations, and held up in sensitivity analyses designed to test the reliability of the finding.
Some studies have also reported improvements in survival and immune function, though this evidence is less consistent. The extracts appear to work in part by stimulating the immune system: the key active compounds, known as lectins, can trigger immune cells to produce signaling molecules that activate the body’s defenses. These same lectins can also directly cause cancer cells to self-destruct through a process called apoptosis, essentially flipping an internal switch that tells damaged or abnormal cells to die.
How It Works Biologically
Mistletoe’s active components include lectins and small proteins called viscotoxins. The lectins are the most studied. Each lectin molecule has two functional parts: one that attaches to the surface of a cell and helps the molecule get inside, and another that shuts down the cell’s protein-making machinery. When protein production stops, the cell triggers its own death.
This mechanism affects different immune cells to varying degrees. Natural killer cells and certain white blood cells involved in antibody production are the most sensitive, followed by other types of immune cells. In lab studies, mistletoe lectins also stimulate immune cells called monocytes and macrophages to produce inflammatory signaling molecules, which can help the body mount a stronger response against tumors. The lectins increase levels of reactive oxygen species inside cells, another pathway that pushes abnormal cells toward death.
These effects have been well documented in laboratory and animal studies. Translating them into clear-cut clinical benefits in humans has been more complex, which is part of why regulatory agencies have taken different positions on mistletoe therapy.
Regulatory Status
In several European countries, mistletoe extracts are available as prescription or over-the-counter medications, sold under brand names like Iscador, Helixor, and abnobaVISCUM. They’re integrated into mainstream cancer care, often used alongside chemotherapy and radiation.
In the United States, the picture is different. The FDA has not approved mistletoe extracts as a treatment for cancer or any other medical condition. Injectable mistletoe is not commercially available through standard channels, though some integrative oncology practitioners use it. This regulatory gap means that most Americans encounter mistletoe only as a holiday decoration, not a therapy.
Safety and Toxicity
Both American and European mistletoe can be toxic in high doses, though neither has been shown to cause liver injury at the doses used in therapeutic settings. The bigger concern is accidental ingestion, particularly by children.
A retrospective study of mistletoe ingestion cases found that symptoms were infrequent even when people swallowed 5 to 20 berries or 1 to 5 leaves. When symptoms did occur, they were typically mild: gastrointestinal upset, drowsiness, or eye irritation. However, more serious reactions are possible. One infant who ingested both berries and leaves experienced a seizure, and another toddler developed problems with coordination. Small children are at highest risk because of their low body weight.
When used as a prescribed injectable therapy in Europe, the most common side effects are mild: redness and swelling at the injection site, low-grade fever, and flu-like symptoms. These reactions are generally interpreted as signs that the immune system is responding to the extract.
The Holiday Tradition
For most people searching about mistletoe, the familiar context is the holiday custom of kissing beneath a sprig hung in a doorway. This tradition has roots in Norse mythology and was well established in England by the 18th century. The plant’s evergreen leaves and white berries, appearing in winter when most plants are dormant, gave it symbolic associations with fertility and vitality long before anyone studied its chemistry. American mistletoe is the species typically sold for decoration during the holidays, and it remains far more common in U.S. households as an ornament than as anything medicinal.