Mistletoe Extracts

by National Cancer Institute

Mistletoe is a plant that grows on various types of trees and has been used to treat a number of disorders.

Laboratory studies have suggested that mistletoe may enhance the activity of immune system cells so that they release more of the chemicals that damage cancer cells.

Animal studies have suggested that mistletoe may be useful in decreasing the side effects of conventional cancer therapy.

The literature that is available on clinical trials consists of anecdotal reports, case series, and a few clinical trials that have yielded inconclusive results.

The U.S. Food and Drug Administration has not found mistletoe products to be safe and effective in treating cancer in humans.

Questions and Answers About Mistletoe

1. What is mistletoe?

Mistletoe is a plant that grows on various types of trees, including apple, oak, maple, elm, pine, and birch. It has been used for centuries to treat a number of disorders such as epilepsy, hypertension, headaches, menopausal symptoms, infertility, arthritis, and rheumatism. Mistletoe is used mainly in Europe and Asia, where commercially available products are marketed under the brand names Iscador, Eurixor, Helixor, Isorel, Vysorel, and ABNOBAviscum. Mistletoe products are not sold commercially in the United States.

The chemical composition of commercial mistletoe products varies, depending on the type of tree on which the mistletoe plant grew, the time of year the plant was harvested, the species of mistletoe, how it was prepared, and the commercial producer. This summary discusses research conducted primarily with a mistletoe species known as Viscum album Loranthaceae.

Mistletoe extracts are prepared as water-based solutions or solutions of water and alcohol. Mistletoe products can be subdivided according to the type of tree on which the plant grew: for example, IscadorM is obtained from apple trees, IscadorP comes from pine trees, IscadorQ is obtained from oak trees, and IscadorU comes from elm trees.

2. What is the history of the discovery and use of mistletoe as a complementary or alternative treatment for cancer?

Mistletoe was reportedly used by the Druids and the ancient Greeks, and mistletoe appears in legend and folklore as a "cure-all." Interest in mistletoe as a potential treatment for cancer began in the 1920s.

Extracts of mistletoe have been shown to kill cancer cells in the laboratory and to stimulate the immune system (the complex group of organs and cells that defends the body against infection or disease). Because of its ability to stimulate the immune system, mistletoe has been classified as a type of biological response modifier (a substance that stimulates the body's response to infection and disease).

Components of mistletoe that have been studied for their usefulness in treating cancer include alkaloids, viscotoxins, and lectins. Some studies have indicated that the lectin known as ML-I (or viscumin) may be one of the active components of mistletoe. Other studies have suggested that the active components in mistletoe may be the alkaloids and viscotoxins.

3. What is the theory behind the claim that mistletoe is useful in treating cancer?

Mistletoe is a semiparasitic plant and holds interest as a potential anticancer agent because extracts derived from it have been shown to kill cancer cells in vitro and to stimulate immune system cells both in vitro and in vivo. Two components of mistletoe, namely viscotoxins and lectins, may be responsible for these effects. Refer to the PDQ health professional summary on Mistletoe Extracts 6 for more information on theory.

4. How is mistletoe administered?

Mistletoe extracts are given by injection into the muscle (intramuscular), beneath the skin (subcutaneous), or into a vein (intravenous or IV).

5. Have any preclinical (laboratory or animal) studies been conducted using mistletoe?

Laboratory and animal studies have been conducted with mistletoe, either alone or in combination with other agents. Findings from laboratory studies have suggested that mistletoe may enhance the activity of immune system cells so that they release more of the chemicals that damage cancer cells.

Animal studies assessing mistletoe's ability to stop cancer cell growth have had different results depending on the extract used, the dose, how it was given, and the type of cancer studied. Results of a few animal studies have suggested that mistletoe may be useful in decreasing the side effects of conventional cancer therapy, such as chemotherapy and radiation therapy, and that it may counteract the effects of drugs used to suppress the immune system.

6. Have any clinical trials (research studies with people) been conducted using mistletoe?

Despite the fairly widespread use of mistletoe in Europe and Asia, few clinical trials have been conducted. The literature that is available has been published primarily in non-English language journals. It consists of anecdotal reports (incomplete descriptions of the medical and treatment history of one or more patients), case series (a group or series of case reports involving patients who were given similar treatment), and a few clinical trials that have yielded inconclusive results.

Most research into the use of mistletoe has focused on its effects on the immune system. Although there is substantial information about mistletoe's ability to affect the immune system, there is no evidence that this enhanced immunity leads to increased destruction of cancer cells.

A few clinical trials of mistletoe lectin (a component of mistletoe) are taking place in Europe. The PDQ clinical trials database contains protocol abstracts for clinical studies of mistletoe as a treatment for cancer.

7. Have any side effects or risks been reported from mistletoe?

The side effects associated with mistletoe products have been minimal. Most commonly seen side effects are injection site reactions and less commonly fever and flu-like symptoms.

Mistletoe plants and berries, however, are toxic to humans. Side effects associated with eating mistletoe plants and berries include seizures, slowing of the heart rate, abnormal blood pressure, vomiting, and death. A few cases of severe allergic reactions, including anaphylactic shock, have been reported. The severity of these toxic effects may depend on the amount consumed and the type of mistletoe plant eaten.

8. Is mistletoe approved by the U. S. Food and Drug Administration (FDA) for use as a cancer treatment in the United States?

The FDA has not found mistletoe products to be safe and effective in treating cancer in humans.

To conduct clinical drug research with humans in the United States, researchers must file an Investigational New Drug (IND) application with the FDA. IND approval is also required for clinical investigation of homeopathic drugs. The FDA does not disclose information about IND applications or approvals; this information can be released only by the applicants. At present, at least 2 U.S. investigators have IND approval to study mistletoe as a treatment for cancer. The mistletoe extracts discussed in this summary are sold in various countries as drugs, but they are not approved by the FDA for sale in the U.S.

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