Several constituents have been shown to contribute to the medicinal action of mistletoe. Most notable are mistletoe lectins (also called viscotoxins), choline derivatives, alkaloids, polypeptides, and polysaccharides. Human pharmacological studies have found that mistletoe extract given by injection stimulates immune system function.^{4, 5, 6} Some test tube and animal studies suggest that certain mistletoe constituents, including the alkaloids, can also kill cancer cells.^{7, 8} Numerous clinical trials have found that subcutaneous injections of mistletoe extracts can help people with cancer of various organs, though some have also failed to show any benefit.^{9, 10} There is no evidence that people with cancer would benefit from receiving mistletoe orally.

Mistletoe’s other uses have been less rigorously studied. Preliminary trials carried out using oral mistletoe have found it can reduce the symptoms of high blood pressure, particularly headaches and dizziness.^{11, 12} However, mistletoe has a small (if any) effect on actually lowering blood pressure.¹³

Test tube and animal studies suggest that mistletoe extracts can stimulate insulin secretion from pancreas cells and may improve blood sugar levels in people with diabetes.^{14, 15} Given both mistletoe’s tradition around the world for helping people with diabetes and these promising preclinical results, human clinical trials are needed to establish mistletoe’s potential for this condition.