Article submitted by Dr. Heather Woodward, Clinical Pharmacist

Dietary supplements include a diverse range of products. From vitamins, minerals and herbs, to protein powders, fish oil and probiotics, it’s a lucrative $30 billion dollar industry.  The Centers for Disease Control and Prevention (CDC) estimates that over half of the U.S. population takes one or more dietary supplements. In those diagnosed with or recovering from cancer, this estimate dramatically increases. Both cancer itself and various treatments (radiation, chemotherapy) can cause intolerable short term and even chronic side effects that may not respond to conventional medicine. It’s no wonder patients seek alternative therapies for relief.

A review of the clinical trials supporting or refuting the evidence of dietary supplement use is beyond the scope of this blog post. Whether or not they work isn’t the most important issue. The larger concern is that a high percentage of cancer patients start a supplement without telling their doctor.  Many people assume that natural herbs and vitamins are safe because they are present in, or produced by, nature.  This is not always the case for several reasons.

First of all, companies who make dietary supplements do not need to prove their product is safe before it ends up in your medicine cabinet. The FDA requires companies to follow manufacturing guidelines, however, enforcement of guidelines is limited due to the sheer number of manufacturers and products. Some supplements are made in clean, controlled labs and labeled accurately. Others are made less carefully and can contain different herbs, fillers and even prescription drugs that are not listed on the label. Common reported contaminants include heavy metals like arsenic and mercury, pesticides, bacteria, dust and mold. Unfortunately, recalled or unsafe products can take months or years to remove from shelves.

Prolonged use or large doses of dietary supplements can cause undesirable side effects and even serious harm.  For instance, too much zinc or vitamin C can cause nausea, stomach cramps and diarrhea. High doses of selenium can lead to hair loss, fatigue and mild nerve damage. Niacin (B3) and vitamin A have been known to cause liver damage. Some supplements have even caused liver failure requiring transplant.

Importantly, supplements can interact with anti-cancer treatments. For example, St. John’s wort can decrease the amount of time that the anti-cancer medication Gleevec® (imatinib) remains at therapeutic blood levels by 44%. Green tea leaf extract or, epigallocatechin-3-gallate (EGCG), has been shown to increase the gastrointestinal toxicity of irenotecan and also block the effects of bortezomib. Similar interactions with chemotherapy and radiation have been reported with the use of turmeric, ginseng, vitamin C…and the list goes on.

To harness the benefit of dietary supplements and avoid harm, follow these helpful tips:

  • Have a conversation with your doctor or pharmacist. Communication is key. Your healthcare provider needs to be in on key decisions you make so that you can continue to navigate the journey as a team.
  • Look for the USP symbol on the label (U.S. Pharmacopeial Convention).  A USP-verified product contains the listed ingredient at the listed strength on the label. It also means the product does not contain contaminants like microbes or heavy metals.
  • More information on USP verified supplements can be found here and here.
  • Buy products made in the United States. Compared to products imported from countries with little or no oversight on the manufacturing process, products made in the U.S. are potentially safer.
  • Become an educated consumer. It’s difficult to navigate the sea of information on the internet. Trusted information on the use of dietary supplements can be found through these links: Memorial Sloan Kettering Cancer CenterNational Institutes of Health Dietary Supplement Label DatabaseThe National Cancer InstituteThe George Washington University Complementary and Alternative Medicine Website.

1. Kantor E et al. Trends in Dietary Supplement Use Among US Adults from 1999-2012. JAMA. 2016 Oct;316(14):1464-74.

2. Cohen P. The Supplement Paradox: Negligible Benefits, Robust Consumption. JAMA. 2016 Oct;316(14):1453-54.

3. John G et al. Complementary and Alternative Medicine Use Among US Cancer Survivors. Cancer. 2016 Feb;(10122:598-610

4. US Food Drug Administration. Dietary supplement products & ingredients. Updated January 13, 2016. Available at:
Accessed November 15, 2016.

5. Wright R, Baccareli  A. Metals and Neurotoxicology. J Nutr. 2007;137:2809-2813.

6. Posadzki P, Watson L and Ernst E. Contamination and adulteration of herbal medicinal products (HMP): an overview of systematic reviews. Eur J Clin Pharmacol. 2013 Mar;69(3):295-307.

7. Stournaras E and Tziomalos K. Herbal medicine-related hepatotoxicity. World J Hepatology. 2015;7(19):2188-2193.

8.Goon CP et al. UGT1A1 Mediated Drug Interactions and its Clinical Relevance. Curr Drug Metab. 2016;17(2):100-6.

9. Lee SH, Ahn YM, Ahn SY, Doo HK, Lee BC. Interaction between warfarin and Panax ginseng in ischemic stroke patients. J Altern Complement Med. 2008 Jul;14(6):715-21. PMID: 18637764

10. Golden EB, Lam PY, Kardosh A, et al. Green tea polyphenols block the anticancer effects of bortezomib and other boronic acid-based proteasome inhibitors. Blood. 2009 Jun 4;113(23):5927-37.

11. Lin LC, Wang MN, Tsai TH. Food-drug interaction of (-)-epigallocatechin-3-gallate on the pharmacokinetics of irinotecan and the metabolite SN-38. Chem Biol Interact. 2008 Aug 11;174(3):177-82.

12. Bayet-Robert M, Kwiatkowski F, Leheurteur M, et al. Phase I dose escalation trial of docetaxel plus curcumin in patients with advanced and metastatic breast cancer. Cancer Biol Ther. 2010 Jan;9(1):8-14.

13. Epelbaum R, Schaffer M, Vizel B, Badmaev V, Bar-Sela G. Curcumin and gemcitabine in patients with advanced pancreatic cancer. Nutr Cancer. 2010;62(8):1137-41.

14. Zhang W, Lim LY. Effects of spice constituents on P-glycoprotein-mediated transport and CYP3A4-mediated metabolism in vitro. Drug Metab Dispos. 2008 Jul;36(7):1283-90.

All content found on the website, including: text, images, audio, or other formats were created for informational purposes only. The Content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this Website. If you think you may have a medical emergency, call your doctor, go to the emergency department, or call 911 immediately. Links to educational content not created are taken at your own risk.