Mistletoe is a semi-parasitic plant that grows on various host trees. Extracts of this plant are used for a variety of conditions including cancer, HIV, hepatitis, and degenerative joint disease. Oral preparations are available as dietary supplements and homeopathic remedies. However, research reported in the literature has only evaluated parenterally administered formulations thus far, which are not approved for use in the United States by the Food and Drug Administration.
In animal models, mistletoe injections attenuated airway inflammation and eosinophil infiltration (1). An injectable form of mistletoe lectins reduced frequency and intensity of clinical signs and symptoms of hepatitis C (2), although little has been added to the literature since this earlier study. There are no published trials evaluating mistletoe for HIV or arthritis.
Mistletoe extracts have been noted to have anticancer effects in animal models (3) (4). Earlier studies in humans support the use of mistletoe for cancer supportive care to improve symptoms, reduce chemotherapy and radiotherapy side effects, and prolong survival (5) (6) (7). Epidemiologic data also suggest a survival advantage following mistletoe treatment (8) (9).
In more recent studies, simultaneous exposure of various cancer cell lines to mistletoe extract along with doxorubicin, gemcitabine, docetaxel, or cisplatin does not appear to inhibit chemotherapy and may produce additive effects (10). In human studies, mistletoe improved cancer-treatment related toxicities in patients with advanced non-small cell lung cancer (11) and colorectal cancer (12), and reduced symptoms and improved quality of life (QoL) in patients with pancreatic (13) and breast (14) cancers. In two studies with 5-year follow-ups of breast cancer patients, mistletoe did not appear to negatively influence chemotherapy efficacy (14) and appeared to continue reductions in persistent symptoms (15). Mistletoe administered in conjunction with gemcitabine in patients with advanced solid tumors allowed higher gemcitabine doses to be used without apparent effects from mistletoe on gemcitabine pharmacokinetics (16). Although mistletoe appeared to prolong survival in patients with locally advanced or metastatic pancreatic cancer (13), no significant survival effects were found in older studies for patients with metastatic colorectal cancer (17), melanoma (18), or head and neck cancer (19).
Raw mistletoe contains toxic constituents. Possible adverse effects from mistletoe treatment include injection site reactions, chills, and fever (16) (20). Long-term use may also reduce T-cell function in cancer patients (21), but the majority of adverse reactions were mild to moderate and dose-related (22). Because mistletoe inhibits CYP3A4 in vitro, it could theoretically interact with drugs metabolized by this enzyme (23).