Mistletoe

Mistletoe grows as a partial parasite on a variety of trees—particularly pine, apple, plum, poplar, and spruce—across northern Europe and Asia. The young leafy twigs with flowers are used. Mistletoe’s white berries are potentially toxic and should be avoided. American mistletoe, various species of Phoradendron, are similar but have not been widely studied. They should not be substituted for European mistletoe until more information is available.

The ancient Druids of northern Europe and other pagan groups revered mistletoe, particularly when it infected oak trees (a rare occurrence). Over time, this reverence of mistletoe was translated into the Christian ritual of hanging mistletoe over doorways at Christmas. The custom of kissing under the mistletoe may be a remnant of pagan orgies held before mistletoe altars.¹

The name mistletoe is said to derive from the Celtic word for “all-heal.” This correlates with its historical use for everything from nervous complaints to bleeding to tumors.² It is difficult to categorize all of the uses of mistletoe, particularly when one looks at the vast number of uses for this herb in traditional Chinese and Korean medicine. In the early 20th century, Rudolf Steiner created what is known as anthroposophical medicine. This mystical system used a variety of unusual remedies, including special extracts of mistletoe for injection. Steiner helped bring mistletoe into the modern era of scientific research, particularly as a potential treatment for cancer.³

Several constituents have been shown to contribute to the medicinal action of mistletoe. Most notable are mistletoe lectins (also called viscotoxins), choline derivatives, alkaloids, polypeptides, and polysaccharides. Human pharmacological studies have found that mistletoe extract given by injection stimulates immune system function.^{4, 5, 6} Some test tube and animal studies suggest that certain mistletoe constituents, including the alkaloids, can also kill cancer cells.^{7, 8} Numerous clinical trials have found that subcutaneous injections of mistletoe extracts can help people with cancer of various organs, though some have also failed to show any benefit.^{9, 10} There is no evidence that people with cancer would benefit from receiving mistletoe orally.

Mistletoe’s other uses have been less rigorously studied. Preliminary trials carried out using oral mistletoe have found it can reduce the symptoms of high blood pressure, particularly headaches and dizziness.^{11, 12} However, mistletoe has a small (if any) effect on actually lowering blood pressure.¹³

Test tube and animal studies suggest that mistletoe extracts can stimulate insulin secretion from pancreas cells and may improve blood sugar levels in people with diabetes.^{14, 15} Given both mistletoe’s tradition around the world for helping people with diabetes and these promising preclinical results, human clinical trials are needed to establish mistletoe’s potential for this condition.

Traditionally a cold water extract (cold infusion) is made by soaking 2–4 teaspoons (10–20 grams) of chopped mistletoe in two cups (500 ml) of water overnight.¹⁶ This is taken first thing in the morning and can be sweetened with honey. Another batch is left to steep during the day and drunk at bedtime. Alternately a hot tea can be made by infusing 1 teaspoon (5 grams) of leaves in a cup (250 ml) of just-boiled water for 5–10 minutes. Two cups (500 ml) are consumed per day.¹⁷ A tincture, approximately 1/8 teaspoon (1/2 ml) three times per day, can also be used.

At least three standardized, injectable extracts have been studied in Europe: Iscador, Helixor, and Eurixor. These products are not designed for self-treatment and are not commercially available in the United States. Iscador is the only fermented extract of the three, and each is standardized in a different way, making comparisons between the extracts difficult. In addition, there are different forms of each extract taken from mistletoe growing on different host trees. Typically, one weekly injection providing 1 mg of mistletoe lectin I per kilogram of body weight is given. People interested in subcutaneous or other injectable forms of mistletoe should consult with a physician.

In the recommended oral amounts, mistletoe is rarely associated with side effects.¹⁸ Two reports, however, have confirmed the danger of ingesting mistletoe leaves and berries in large quantities, particularly when children accidentally eat the berries at Christmas.^{19, 20} Many of these exposures involved American mistletoe and not European mistletoe. European mistletoe is less toxic than the American species. If six to twenty berries or four to five leaves are eaten, then activated charcoal or ipecac can be used at home to induce vomiting. Emergency room care is only indicated if more than 20 berries or five leaves are ingested or if symptoms develop at lower levels of exposure. Possible symptoms of overdose are nausea, vomiting, low blood pressure, or dizziness.

Injectable forms of mistletoe may cause local redness and pain but otherwise have rarely been associated with serious side effects. There is one case report of a severe allergic reaction to an injected mistletoe preparation.²¹ Mistletoe is not recommended for use in children, or for women during pregnancy or breast-feeding.