Mistletoe has been used medicinally for over 2,000 years, and today it’s most notable as a complementary cancer therapy widely used in parts of Europe. But its applications stretch from ancient treatments for epilepsy and fertility to modern research into immune stimulation. There are also important safety distinctions between the two main types, and between the holiday decoration hanging in your doorway and the pharmaceutical-grade extracts used in clinics.
Two Different Plants, Two Different Uses
When people say “mistletoe,” they could mean one of two plants. American mistletoe is the species sold as a Christmas decoration in the United States. European mistletoe is the species with a long medicinal history and the one used in modern clinical research. Both are semiparasitic plants that grow on host trees, and both contain potentially harmful compounds, but their chemical profiles differ enough that they aren’t interchangeable.
European mistletoe contains three groups of biologically active compounds: small toxic proteins that can kill cells directly, complex sugar-protein molecules (lectins) that bind to immune cells and change their behavior, and polysaccharides that may further stimulate the immune system. American mistletoe shares some of these compounds but has not been studied nearly as extensively for medical use. The holiday sprigs you see at the store are almost always American mistletoe and are not suitable for any medicinal purpose.
Ancient and Traditional Medicine
Mistletoe has one of the longest documented histories of any medicinal plant. Hippocrates used it around 400 BC to treat spleen disorders and menstrual complaints. The Roman physician Celsus, writing in the first century AD, applied mistletoe preparations to reduce swollen lymph nodes in the neck. Dioscorides included it in his influential herbal guide as a treatment for epilepsy, and Pliny the Elder described how the Druids considered mistletoe growing on oak trees sacred, believing its juice could restore fertility in barren animals and serve as a universal antidote to poison.
The epilepsy connection persisted for centuries. In 1719, the English physician John Colbatch published a book-length argument for mistletoe as a remedy for convulsive disorders, reporting that it reduced heart rate, calmed fits, and lengthened the time between seizures. While these traditional uses have largely been replaced by modern pharmaceuticals, they helped establish mistletoe as a plant worth investigating scientifically.
Mistletoe in Cancer Care
The most significant modern use of mistletoe is as a complementary therapy alongside conventional cancer treatment. In Germany, Austria, and Switzerland, mistletoe extracts are among the most commonly prescribed complementary medicines for cancer patients. The therapy is not meant to replace chemotherapy, radiation, or surgery. Instead, it’s used alongside those treatments, primarily to improve quality of life during the difficult months of conventional therapy.
Lab studies have shown that mistletoe extracts can kill cancer cells directly, slow tumor cell migration and invasion, and boost the activity of natural killer cells (a type of immune cell that targets tumors). These findings come from both test-tube experiments and animal studies. The National Cancer Institute notes that mistletoe extracts can activate immune cells and suppress genes involved in tumor progression, which forms the scientific basis for continued clinical interest.
In practice, patients typically receive mistletoe as injections under the skin, starting at a low dose that gradually increases to assess tolerability. Some clinics also offer intravenous infusions. Treatment can last anywhere from a few months to several years depending on the individual response. Common side effects of the injections include redness and swelling at the injection site, mild fever, flu-like symptoms, fatigue, and occasionally headache or diarrhea. Intravenous infusions carry similar side effects, sometimes with mild itching or weakness.
Regulatory Status
Mistletoe extracts are not approved as a cancer drug in the United States. However, they are not banned either. Johns Hopkins University launched the first FDA-approved clinical trial of intravenous mistletoe, publishing initial results in 2023. Mistletoe preparations represent a notable share of cancer-related botanical drug investigations submitted to the FDA, with several advancing to later-phase trials. Still, the FDA has approved only two botanical drugs of any kind since 1984, so the regulatory path is narrow.
In Europe, the situation is quite different. Mistletoe extracts are available by prescription in several countries and are covered by some national health insurance plans. This gap between European clinical practice and U.S. regulatory status is one of the more unusual divides in modern oncology.
Toxicity and Accidental Ingestion
Raw mistletoe is poisonous. The toxic compound phoratoxin is found in all parts of the plant but is most concentrated in the leaves. If a child or pet eats mistletoe berries or leaves, the typical symptoms include nausea, vomiting, stomach pain, diarrhea, blurred vision, drowsiness, and general weakness. These symptoms usually last one to three days and may require a hospital visit, though death from mistletoe ingestion is unlikely.
This is an important distinction: the pharmaceutical-grade extracts used in clinical settings are carefully prepared and dosed. Eating raw mistletoe from a holiday decoration is not the same thing and can make you sick. If you have mistletoe in your home during the holidays, keep it out of reach of children and pets.
Who Should Avoid Mistletoe Therapy
European mistletoe extracts are considered probably unsafe during pregnancy. There is not enough data to determine safety during breastfeeding. Because mistletoe stimulates the immune system, it may interact unpredictably with immunosuppressive medications or autoimmune conditions. Anyone taking prescription medications should discuss potential interactions before starting mistletoe therapy, as some herbs and drugs interact in harmful ways that aren’t always obvious.