European Mistletoe (Viscum album) extracts have been used as complementary therapy for cancer patients, particularly in parts of Europe, to alleviate chemotherapy side effects such as fatigue, nausea, and reduced quality of life. The scientific basis for these uses is mixed but growing. Multiple randomized and non-randomized clinical trials, primarily conducted in Germany and Switzerland, suggest that mistletoe extracts may improve quality of life, reduce chemotherapy-induced side effects, and possibly enhance immune parameters in cancer patients. Notable systematic reviews and meta-analyses (e.g., Cochrane reviews) have found that while some studies report positive effects on symptoms and quality of life, methodological limitations such as small sample sizes, lack of blinding, and heterogeneity of preparations limit the strength of these conclusions.

Mistletoe extracts contain lectins and other compounds believed to modulate the immune system and induce apoptosis in cancer cells in vitro. However, robust evidence for direct effects on tumor progression in humans is lacking. Regulatory bodies, such as the European Medicines Agency, acknowledge the use of mistletoe in supportive cancer care but do not endorse it as a replacement for standard chemotherapy. In summary, while scientific evidence exists supporting the use of European Mistletoe to reduce chemotherapy side effects, it is not universally accepted, and more rigorous, large-scale trials are needed to confirm its efficacy and safety.