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Nutrition and daily life

Is natural always safe? Herbs, supplements and the value of asking

"It’s natural, so it can’t hurt" is a common belief. But many of the strongest medicines come from plants, and some plants are poisonous. This section explains how to approach natural products during treatment.

Last updated: ~1 min read
Herbs and a mushroom on a dark table, half in shadow.
Figure 1.Natural can help or harm.

01Short answer

No, natural is not always safe. Herbs and supplements can interact with chemotherapy, harm the liver and kidneys, and raise bleeding risk. Some products contain substances not listed on the label, or contaminants. There is concern that antioxidant supplements may weaken some treatments. Before starting any new product, ask your oncologist or pharmacist.

02Simple explanation

Natural ≠ safe.

Herbs can affect medicines.

Supplements may have hidden substances.

Ask before starting.

03Scientific explanation

Examples: St John’s wort lowers levels of chemotherapy drugs; green tea extract affects bortezomib; some herbs can damage the liver.

NCI: there is no evidence that herbal infusions treat leukemia.

MSK: herbal products can affect how the liver breaks down medicines, so tell your oncologist.

04What happens in the body?

Why can it be dangerous?

Plant compounds affect the liver enzymes that break down medicines, so a drug may become weaker or toxic.

A purple foxglove flower.
Figure 2.A beautiful but potent plant.

How to ask

Bring all the packs to your appointment; your doctor and pharmacist can check them against your medicines.

Bottles in shadow at one end of a desk, a stethoscope at the other.
Figure 3.Discuss supplements with your doctor.

Safe brewing

Sealed bag, freshly boiled water, 5 minutes covered, drink hot. Do not drink an infusion that has stood for hours.

With medicines

1–2 cups of a mild infusion a day usually cause no problems; capsules and extracts only with your doctor.

05Brewing: four steps

Sealed bag, swap market herbs, boiling water, drink hot.

Sealed bag — Factory-made.1Sealed bagFactory-made.
Not loose — A bag instead.2Not looseA bag instead.
Boiling water — Covered.3Boiling waterCovered.
Drink soon — Do not keep.4Drink soonDo not keep.
ComfortA warm drink.
FluidsThrough the day.
SafetyBoiling water.

06Key points at a glance

TopicIn brief
Why can it be dangerous?Plant compounds affect the liver enzymes that break down medicines, so a drug may become weaker or toxic.
How to askBring all the packs to your appointment; your doctor and pharmacist can check them against your medicines.
Safe brewingSealed bag, freshly boiled water, 5 minutes covered, drink hot. Do not drink an infusion that has stood for hours.
With medicines1–2 cups of a mild infusion a day usually cause no problems; capsules and extracts only with your doctor.

07Key terms

St John’s wort
A plant with strong interactions with many medicines.
Antioxidant
A substance that reduces oxidation.
Infusion
A herb steeped in boiling water.
Extract
A concentrated plant substance.
Neutropenia
Low neutrophils.

08Key points

  • Natural is not always safe.
  • Tell your doctor about every supplement.
  • Do not trust miracle claims.
  • Sealed bag and boiling water.
  • Capsules only with your doctor.

09Frequently asked questions

Why is my doctor against supplements?

To protect your treatment; ask the reason and decide together.

Are vitamins dangerous too?

Ordinary doses are often fine, high doses may not be; check with your doctor.

Does this infusion treat leukemia?

No. It is a warm, pleasant drink, not a treatment.

10Questions for your doctor

Take these questions to your appointment. The ones you save are collected on the “My questions” page and stay on this device only.

  1. Why is my doctor against supplements?

  2. Are vitamins dangerous too?

  3. Does this infusion treat leukemia?

My questions

12Sources

  1. National Cancer Institute. Complementary and Alternative Medicine for Patients
  2. National Center for Complementary and Integrative Health (NIH). Herbs at a Glance
  3. Memorial Sloan Kettering Cancer Center. About Herbs, Botanicals & Other Products
  4. Leukemia & Lymphoma Society. Diet Guidelines for Immunosuppressed Patients
  5. National Cancer Institute. Complementary and Alternative Medicine
  6. MedlinePlus. Herbal Medicine
  7. National Cancer Institute (NCI). Eating Hints: Before, during, and after Cancer Treatment
  8. Journal of Clinical Oncology, 2022. Exercise, Diet, and Weight Management During Cancer Treatment: ASCO Guideline
  9. Medicine & Science in Sports & Exercise, 2019. Exercise Guidelines for Cancer Survivors: Consensus Statement from International Multidisciplinary Roundtable
  10. Cochrane Database of Systematic Reviews, 2019. Aerobic physical exercise for adult patients with haematological malignancies
Medical disclaimerThis information is for educational purposes only and does not replace medical advice.
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