European mistletoe, famous during the Christmas season, is a semiparasitic plant that grows on trees in Europe and Asia. Its young leafy twigs and flowers were used as an “all-heal” or panacea, said to be helpful for virtually all diseases. The herb is also said to have played a role in Celtic religious celebrations.

Note: American mistletoe,Phoradendron leucarpum, is related to European mistletoe, but it is thought to be more toxic and has not been well studied.

In the 20th century, mistletoe became popular in Germany through the advocacy of a mystic and philosopher named Rudolf Steiner. The school of medicine he founded, anthroposophical medicine, recommended injectable forms of mistletoe as a treatment for cancer. The initial basis for this use was Steiner’s “clairvoyant” insight. Scientific tests were subsequently conducted with somewhat positive results, but current evidence is far from definitive.

Mistletoe extracts show anticancer effects in the test tube.1-5However, test-tube studies cannot show a treatment effective; only controlled clinical trials can do that. A 2003 review found 10 human trials of injected mistletoe for cancer that met at least minimal scientific standards.6Unfortunately, even these studies generally suffered from significant weaknesses in design. The review authors noted that the better-designed studies failed to find evidence of benefit, in terms of lengthened remission, improved quality of life, or chance of survival. Subsequent human trials have also failed to reach adequate levels of scientific rigor or clinical relevance and have, therefore, failed to clarify matters.7-10, 21,22,24Another review of 21 clinical trials found no convincing evidence that mistletoe was effective for cancer survival, tumor response, quality of life, psychological distress, or any other favorable outcomes.23However, two of the better designed studies did suggest some benefit for breast cancer patients undergoing chemotherapy. A more recent review of 49 22 studies found the addition of mistletoe to standard cancer treatment was associated with improved survival in cancer patients. An analysis restricted to randomized controlled trials, however, showed less of an overall effect.25In a small randomized trial of 32 patients with gastric cancer, addition of mistletoe to oral chemotherapy improved quality of life and reduced the incidence of diarrhea compared to patients who did not receive mistletoe.26

Oral uses of mistletoe have not undergone significant study. Very weak evidence, too weak to rely upon at all, hints that constituents of mistletoe might potentially offer benefit in diabetes11-14 and coldsand flus.15,16 It is commonly stated that oral mistletoe products reduce blood pressure, but there is no scientific evidence to support this belief.