Supplements and cancer: what the evidence says

Vitamins, NAD+ boosters, creatine, herbs and remedies sold for cancer, 28 in all, rated like everything else on this site: a verdict on what studies found, and a rung for how sure the science is. Safety during treatment comes first.

Before you take anything

Tell your care team about every supplementSome supplements and herbs can affect chemotherapy, radiation or other treatment, or be harmful alongside it.Sources: NCCIH: cancer and complementary health approaches; National Cancer Institute: mistletoe extracts (PDQ), June 2023
Some are known to interfereSt. John’s wort weakens several cancer drugs. High-dose antioxidant pills during breast cancer chemotherapy were linked to more recurrence. Probiotics weakened the response to immunotherapy in mice.Sources: Mathijssen et al., St. John's wort and irinotecan, JNCI 2002; SWOG S0221 supplement analysis, JCO 2020 (ASCO Post summary); Dietary fiber, probiotics and melanoma immunotherapy, Science 2021 (ASCO Post)
Supplements aren’t approved before they’re soldThe FDA doesn’t approve dietary supplements as safe or effective, and what’s in a product can vary between brands and batches.Sources: National Cancer Institute: milk thistle (PDQ), November 2022; National Cancer Institute: medicinal mushrooms (PDQ), July 2024
Some cause harmThe supplements below with a safety note, and the full list on What to avoid.

All 28 supplements, rated

Showing 28 of 28 supplements, strongest evidence first in each group.

Rung 1–5 is how sure the science is, not how big the effect is. How to read these

Linked to lower risk

Studies link these to lower cancer risk. On rungs 1 and 2 the link isn’t confirmed, so the verdict says “may”.2 supplements

Linked to higher risk or harm

Studies link these to higher cancer risk. Those marked dangerous cause direct harm, such as poisoning.4 supplements

Mixed, no benefit or unclear

Mixed effects across cancers, tested and found not to help, or not enough human evidence to say.22 supplements

Also rated

Pills used alongside treatment for a symptom, and vitamin D, whose verdict needs more than one word, are rated in the evidence register.

The foods behind some popular supplements are rated in the food finder.

Traditional herbs are covered on the Ayurveda page, and every food and supplement can be searched together in the food and supplement finder.

Spotted an error? Tell us and we’ll check it against the sources.