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Natural supplements for cancer patients to avoid

The information on this page was reviewed and approved by
Maurie Markman, MD, President, Medicine & Science at CTCA.

This page was updated on August 5, 2021.

Natural supplements—the very words sound healthy. Many times, they are. Adding vitamins, minerals and other natural remedies to your daily regimen can boost some people’s immune system, energy level and overall health. But if you’ve been diagnosed with cancer, and especially if you are undergoing treatment, certain supplements may actually harm you. Some may even counteract anti-cancer treatments like chemotherapy. That’s why it is essential that patients always consult with their oncologists before taking any supplements.

It’s true that some specific herbal and dietary supplements may help boost the effects of cancer treatment and even protect noncancerous cells in some cases.

Selenium, for example, seems to be one element that both protects normal cells against damage from chemotherapy and radiation and enhances the effect of treatment on cancerous cells. It’s found in food sources such as grains, fish, meat and eggs, and is also available in supplement form.

Folic acid, a common supplement, or a slight variation (folinic acid), is a part of some chemotherapy regimens, utilized to counteract chemotherapy toxicity without compromising its therapeutic effects. Depending on the chemotherapy drug used, folic acid may be taken in the week before treatment, or a day after. If folic acid is part of your treatment plan, you should only take what your oncologist has specified.

Ginger, commonly used to treat nausea, vomiting and other gastrointestinal symptoms. However, ginger may not be safe to use with all medications, so consider all the medicine you take before supplementing with ginger. For example, it may change the way blood thinning medications, like warfarin, work.

Overall, caution should be used when considering taking any supplement before or during cancer treatment, especially in light of the lack of research around the benefits of most supplements during chemotherapy.

While some show promise in side effect management, other supplements may be detrimental. Some herbs are thought to have a significant negative effect on how the body metabolizes chemotherapy drugs. These include:

  • Garlic
  • Ginkgo
  • Echinacea
  • Ginseng
  • St. John's wort
  • Kava

Additionally, the polyphenols found in many herbs and teas may affect the enzymes that help process chemotherapy drugs. This may cause resistance to chemotherapy drugs such as:

  • Vincristine
  • Vinblastine
  • Taxanes
  • Anthracyclines
  • Tamoxifen
  • Tyrosine kinase inhibitors

In one small 2019 study of breast cancer patients in the Journal of Clinical Oncology, iron taken during chemotherapy was associated with a higher rate of cancer recurrence, and vitamin B12 taken before and during chemotherapy was associated with a negative effect on survival.

St. John’s wort is a common supplement taken to treat depression, anxiety and sleep disorders, but it has the potential to cause a dangerous interaction with chemotherapy medications.

While evidence is clear about some potential herb-drug interactions, the jury is still out on others, like antioxidants, including:

  • Vitamin D
  • Vitamin E
  • Beta carotene

It’s possible these antioxidants may help your body fight cancer cells, or protect your cells from damage due to cancer treatment. But there’s also evidence that they may make cancer treatment less successful, so more research is needed.

In general, elements in certain herbs and supplements may disrupt the way your body processes chemotherapy drugs, making them either less able to fight cancer cells or more toxic to your body than intended. Others, namely daily multivitamins, don’t appear to have an effect on recurrence or survival. It’s always best to check with your care team before taking any vitamins.

It’s an important message many cancer patients don’t appear to hear enough. One study, published in the journal of the Multinational Association of Supportive Care in Cancer, found that 73 percent of the patients studied had taken herbal supplements within the past 30 days—and 25 percent of chemotherapy patients were taking products suspected of causing adverse reactions when used with chemo. Another big warning sign: The majority of the patients studied, 53 percent, had not consulted their doctors about their supplement use. “Supplements can be useful, when taken under the guidance of a trained health care professional,” says Daniel Kellman, Director of Naturopathic Support at our Atlanta hospital. “But what many people, especially cancer patients, may not know is that some herbal remedies can actually work against them.”

“Many herbal medicines and other nutraceuticals,” Kellman explains, may interfere with how the liver metabolizes chemotherapy drugs. St. John’s wort, a popular plant-based supplement, is one common offender. Used for centuries to combat mild to moderate depression, this plant-based herb is known to increase the production of an enzyme that breaks down certain chemicals and toxins—including many of the agents used in chemotherapy drugs. Other natural supplements that may be detrimental to cancer patients undergoing treatment include:

Grapefruit or grapefruit juice: A popular diet aid, grapefruit inhibits enzymes in the liver and can interfere with beta blockers.

Acai berry: Highly touted for health benefits, this palm fruit may interfere with the effectiveness of certain chemotherapy and radiation treatments for the very reason it is celebrated—its antioxidant properties.

Essiac: An herbal team mixture that combines burdock root, slippery elm inner bark, sheep sorrel and Indian rhubarb root, it is often touted as an anti-inflammatory agent and pain reliever. But it also affects the liver’s metabolic processes, possibly inhibiting the effectiveness of chemotherapy.

B17: Often called by the misnomer “vitamin B17,” this is not a vitamin but a supplement from food sources like laetrile, which is found in apricot and apple seeds. Derived from the apricot kernel and touted without proof as a cancer fighter, Kellman says B17 can “have a poisoning effect on the body” because of an inherent chemical ingredient, amygdalin, which turns into cyanide in the stomach.

Graviola or soursop: A fruit of the graviola tree distinguished by its sweet flesh and flavor, soursop is used to make juice, candy and ice cream. Herbal healers in the Caribbean, Mexico and Central and South America use soursop fruit and graviola leaves to treat stomach ailments, fever, infections and other illnesses, but it has also been linked to unsubstantiated claims that it has anti-cancer properties. Kellman says soursop has not been studied in humans, and when used orally, it may actually be harmful, possibly leading to movement disorders such as Parkinson’s disease and to neurotoxicity when ingested as a tea made from the leaves and stems of the graviola.

Green tea extract: Popular for its antioxidant effects, green tea is thought to help reduce cholesterol and blood pressure, facilitate weight loss and prevent tooth decay, among other uses. But Kellman says it can also interfere with the drug bortezomid (Velcade), commonly used to treat multiple myeloma.

Kellman also advises cancer patients to ignore commercial advertisements that promote the use of various supplements and vitamins, especially those irresponsibly marketed as cancer treatments, urging patients instead to seek the advice of a naturopathic provider or other health care professional trained in working with cancer patients.

Possible side effects from supplements

Selenium, folic acid and probiotics have been found to be safe for use during chemotherapy treatment. However, these supplements still have potential side effects.

  • Selenium: Though it’s known for being nontoxic, selenium taken at extremely high levels may result in diarrhea, nausea, vomiting, fatigue, hair loss, nail discoloration/brittleness, or joint pain.
  • Folic acid: There are few adverse effects related to folic acid. Some neurologic issues have been noted in people who have pernicious anemia.
  • Probiotics: Research is ongoing to confirm whether probiotics are safe. Rarely, people taking probiotics have been found to have unexpected fungi or bacteria in their blood, or endocarditis, inflammation of the lining of the heart chambers and valves, typically from a bacterial infection.

Questions to ask your doctor

Once you let your doctor know about all the medications you take—including over-the-counter drugs, vitamins and other supplements—you may still have more questions, especially when it comes to your cancer treatment.

Below are some questions to consider asking:

  • Can I take my other medications (including prescriptions, over-the-counter drugs, vitamins and other supplements) before and during chemotherapy?
  • What are the potential side effects of this cancer treatment?
  • What can I do besides take supplements to help manage treatment side effects?
  • Are there any natural supplements that safely help relieve side effects from treatment?
  • What are the side effects of any supplements that are safe to take?
  • Are there any warning signs I should be aware of when taking supplements that are considered safe?
  • When is it safe again to take the supplements I usually take?

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