Dietary supplements — vitamins, minerals, antioxidants, and botanicals like turmeric/curcumin, green tea extract, medicinal mushrooms, and European mistletoe — are widely used by people with cancer, often hoping to boost immunity or fight the tumor. The evidence picture is mixed: some may help with specific symptoms, but for most, high-quality human evidence of an anti-cancer benefit is lacking, and a few can be actively harmful during treatment. High-dose antioxidants may blunt the effect of some chemo and radiation; St. John’s wort and others change how the body processes many cancer drugs; and supplements are not tightly regulated, so purity and dose vary. The safest rule: treat supplements like drugs, disclose everything to the oncology team, and never use them in place of proven treatment. Mistletoe and similar remedies are popular but remain unproven as cancer treatments.
Bring every supplement bottle and its dose to the oncology team and ask specifically about interactions with your current treatment. Prefer products tested by third parties for purity. Pause or avoid supplements around chemotherapy, radiation, immunotherapy or surgery unless your team confirms they are safe.
A few supplements may help selected symptoms, but many carry real interaction risks and none replaces treatment. Disclosure to your care team is the single most important safety step.