Derived from the aerial parts, except berries, of the plant, mistletoe preparations are used by patients for a variety of conditions including cancer, HIV, hepatitis, and degenerative joint disease. Polypeptides, including lectins and viscotoxins, are thought responsible for in vitro immune stimulant and tumor inhibition activities (1). Although orally administered products are available, all research reported in the literature has evaluated parenteral formulations of mistletoe, which are not approved for use in the United States by the Food and Drug Administration.
Mistletoe extracts have anticancer effects in vitro (21). But well-designed randomized trials are lacking. A meta-analysis analyzed 11 of these clinical trials conducted before 1994 and showed no benefit from mistletoe (1), but recent systematic reviews point to the accumulating evidence in support of mistletoe while emphasizing the need for well-designed clinical trials (17) (18). Epidemiologic data also suggest survival advantage following treatment with mistletoe (2) (3). When used in conjuction with chemotherapy, a mistletoe extract improved quality of life in a study of breast cancer patients (22). However, mistletoe was not active in metastatic colorectal cancer resistant to 5-fluorouracil and leucovorin (20).
An injectable form of mistletoe lectins was found to reduce the frequency and intensity of clinical signs and symptoms in patients with hepatitis C (4). Confirmed efficacy for other proposed claims is lacking (5) (6).
Possible adverse effects from treatment include injection site reactions (7), chills, fever, headache, leukocytosis, chest pain, orthostatic hypotension, bradycardia, diarrhea, and vomiting (8) (9). In addition, long-term use of mistletoe extracts may reduce T cell function in cancer patients (10). Toxic doses of mistletoe can produce coma, seizures, and death (11). Possible drug interactions include additive hypotensive effect from antihypertensives and antagonism of cardiac glycosides or antiarrhythmics.