Research has shown that extracts of mistletoe can kill cancer cells and stimulate the immune system in the laboratory. There have been some clinical trials done in Europe showing that mistletoe may increase survival and improve quality of life. But the trials either had weaknesses in their design or they didn't have many participants, which raises some doubts about the findings.

Currently, the National Center for Complementary and Alternative Medicine is sponsoring a clinical trial of mistletoe, with a chemotherapy drug called gemcitabine, for cancer. The study is looking at the toxicity, safety and immune system effects of this combination of drugs. The Food and Drug Administration has not approved the use of mistletoe by injection in the U.S., unless it's used as part of a clinical trial.

Side effects and cautions about mistletoe

First and foremost, raw, unprocessed European or American mistletoe is poisonous. It can cause vomiting, seizures, a low heart rate and death. And American mistletoe isn't safe even for use as a medicine.

European mistletoe is thought to be fairly safe when it's been processed as a medicine that's taken according to product directions and under the supervision of a healthcare provider. It can cause itching or redness at the injection site. Fevers or flu-like symptoms are less common side effects.

Source:
The National Center for Complementary and Alternative Medicine