European mistletoe is a semiparasitic plant that grows on several types of trees in temperate regions worldwide. Where the term "mistletoe" is used on this Web page, it refers to European mistletoe. (European mistletoe is different from American mistletoe, which is used as a holiday decoration.)

• Mistletoe has been used for centuries in traditional medicine to treat seizures, headaches, and other conditions.
• Mistletoe is used mainly in Europe as a treatment for cancer.

The leafy shoots and berries of mistletoe are used to make extracts that can be taken by mouth. In Europe, mistletoe extracts are prescription drugs that are given by injection. In the United States, mistletoe by injection is available only in clinical trials.

What the Science Says

• Laboratory studies have found that mistletoe kills cancer cells and stimulates the immune system.
• The use of mistletoe to treat cancer has been studied in Europe in more than 30 clinical trials. Although improvements in survival or quality of life have been reported, almost all of the trials had major weaknesses in their design that raise doubts about the findings. For example, many of the studies had a small number of participants or did not have a control group.
• NCCAM is sponsoring a clinical trial of mistletoe, given in combination with the drug gemcitabine, for cancer. The study will look at toxicity, safety, and immune system effects of mistletoe extract when combined with this chemotherapy drug.

Side Effects and Cautions

• Raw, unprocessed mistletoe is poisonous. Eating raw, unprocessed European mistletoe or American mistletoe can cause vomiting, seizures, a slowing of the heart rate, and even death. American mistletoe is unsafe for medicinal use.
• In countries where commercial mistletoe is available by injection, such as Germany, those extracts are considered to be generally safe when used according to product directions and under the supervision of a health care provider.
• Injected mistletoe extract may cause itching or redness in the area of the injection. Less commonly, side effects may include more extensive skin reactions, low-grade fevers, or flu-like symptoms. There have been very rare reports of more serious allergic reactions, such as difficulty breathing.
• Because mistletoe has not yet been proven to be a safe and effective cancer treatment, it is not advised to be used outside of clinical trials.
• Tell your health care providers about any complementary and alternative practices you use. Give them a full picture of what you do to manage your health. This will help ensure coordinated and safe care.