What Are Dietary Supplements?
Based on the American Cancer Society:
The term “dietary supplement” refers to a wide range of products including vitamins, minerals, herbs and other botanicals, amino acids, enzymes, and more. You can find dietary supplements in many forms such as pills, gummies, powders, liquids, teas, and bars.
Dietary supplements do not need to be tested and approved by the United States Food and Drug Administration (FDA) since they are not intended to treat, diagnose, prevent, or cure diseases.
Why Caution Matters
Experts warn that some supplements may interfere with chemotherapy effectiveness or increase risks.
- Antioxidant use has been linked to a higher risk of cancer recurrence and, to a lesser extent, death.
- Did you know? Turmeric can cause bleeding, nausea, and diarrhea — and ginseng decreases the efficacy of warfarin.
City of Hope / CancerCenter.org recommends AGAINST (meaning don’t take them!) the use of the following supplements when receiving chemotherapy:
- Garlic
- Ginkgo
- Echinacea
- Ginseng
- St. John’s Wort
- Kava
Regulation Gaps
The FDA does not regulate dietary supplements the same way it regulates medications. This means:
- No guarantee of purity or potency
- Possible contamination
- Variable ingredient quality
What the American Cancer Society Says
The ACS recommends avoiding supplements (other than a multivitamin) during chemotherapy.
Why?
- Possible side effects
- Interactions with chemotherapy or radiation
- Lack of standardization and safety oversight
Practical Pearls
✅ Always review supplements with your oncology team, including your medical oncologist and clinical pharmacist.
Communication Tip
Many patients don’t mention supplements unless asked.
Clinicians can ask:
“Can you tell me what pills or supplements you take, even those a few times a week?”
If your physician doesn’t ask — tell them.
Takeaway
Use supplements cautiously — always with your care team’s or medical oncologist’s guidance.
Collaborative review ensures safe, evidence-based cancer care.
Choose brands verified by third parties such as U.S. Pharmacopeia (USP) or ConsumerLab (CL).
References
- Are dietary supplements safe? (2025) — American Cancer Society.
- Yuan CS, Wei G, Dey L, et al. American ginseng reduces warfarin’s effect in healthy patients: a randomized, controlled trial. Ann Intern Med. 2004 Jul 6;141(1):23–7.
- Barton DL, Liu H, Dakhil SR, et al. Wisconsin Ginseng (Panax quinquefolius) to improve cancer-related fatigue: a randomized, double-blind trial, N07C2. J Natl Cancer Inst. 2013 Aug 21;105(16):1230–8.
- Natural supplements to avoid — CancerCenter.org.