The short answer
"Natural" is a marketing word, not a safety rating. Herbs interact with cancer drugs, supplements are not reviewed before sale, and using alternative medicine instead of treatment worsens survival.
Rating: not supported. "Natural" describes where something came from, not whether it is safe or whether it works.
St John's wort induces the CYP3A4 enzyme; in a small crossover study of five patients, it cut levels of irinotecan's active metabolite by 42%.
FDA does not approve dietary supplements before they are sold — manufacturers, not regulators, vouch for safety.
In a 2018 JNCI study, people who used alternative medicine alone for cancers that had not spread had 2.5 times the risk of death.
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The whole article, with every detail and caution.
This page is for people with cancer, and their families, who are weighing natural or alternative remedies. It looks at the claim that natural means safer and what the research shows.
The claim
Plant-based, natural and traditional remedies are gentler and safer than chemotherapy, radiation or surgery. So a natural route is the lower-risk choice.
Why it appeals
The idea appeals for many understandable reasons:
- Conventional treatment sounds frightening, and a herb sounds like food.
- A natural therapy is something you can choose and control, at a moment when very little feels controllable.
- It is often cheaper, or seems to be.
- Someone kind spent an hour listening to you, and a clinic gave you fifteen minutes.
- Plenty of people have good reasons not to give medicine automatic trust: cost, past mistreatment, faith, or a bad experience.
None of that is foolish.
What the evidence shows
"Natural" is not a safety category. Foxglove, hemlock and tobacco are natural. What matters is dose, purity, and what else is in your body at the time.
Herbs can weaken cancer drugs. St John's wort is the clearest example. It speeds up (induces) the liver enzyme CYP3A4, which many cancer treatments depend on. A crossover study in patients receiving irinotecan was published in the Journal of the National Cancer Institute in 2002. Taking St John's wort cut plasma levels of the active metabolite SN-38 by 42%. That is not a side effect. That is less of the drug reaching the cancer. NCCIH lists St John's wort as weakening some cancer medications, including irinotecan. It does the same to warfarin, birth control and HIV drugs.
Supplements are not checked before sale. FDA states it does not have the authority to approve dietary supplements before they are marketed. FDA also says a firm generally does not have to give it evidence of safety before or after marketing a supplement.
Used instead of treatment, the outcomes are worse. Researchers at Yale used the National Cancer Database. They identified 281 people with non-metastatic breast, prostate, lung or colorectal cancer who chose alternative medicine as their only cancer treatment. After 2:1 matching against people who had conventional treatment, the results were published in JNCI in 2018. The alternative-medicine group had 2.5 times the risk of death overall (hazard ratio 2.50). The risk was highest for breast cancer (hazard ratio 5.68).
A companion study in JAMA Oncology the same year looked at people who used complementary medicine alongside treatment. They also had a higher risk of death. But the analysis showed why. They refused surgery, chemotherapy, radiation or hormone therapy at much higher rates. The complementary therapy itself did not explain it.
NCCIH puts the summary plainly. No complementary health approach has been shown to prevent or cure cancer.
What this does not mean
It does not mean everything outside a hospital is useless. NCCIH says some approaches, such as acupuncture, mindfulness-based stress reduction, and yoga, may help manage cancer symptoms and treatment side effects. It does not mean your instinct to look for something more is a character flaw. And it does not mean that if you have already tried something, you have ruined anything.
The line that matters is between alongside and instead of.
The bottom line
"Natural" tells you where something came from. It does not tell you whether it is safe, or whether it works. The specific risks are interactions with your treatment, and products no one checked before selling. The largest risk is delaying or replacing a treatment that could have helped you.
The most useful thing you can do is simple. Bring the actual bottle, or the practitioner's name, to your oncology team, and ask directly. Teams are used to this question. Being told what you are taking helps them far more than being told nothing.
Sources
- Johnson et al., JNCI 2018 — Use of alternative medicine for cancer and its impact on survival
- Johnson et al., JAMA Oncology 2018 — Complementary medicine, refusal of conventional cancer therapy, and survival
- Mathijssen et al., JNCI 2002 — Effects of St John's wort on irinotecan metabolism
- NCCIH — St. John's Wort
- FDA — Questions and Answers on Dietary Supplements
- NCI — Complementary and Alternative Medicine
Common questions
What is the difference between complementary and alternative?
Complementary means used alongside standard treatment, usually for symptoms and quality of life. Alternative means used instead of it. The evidence on harm is overwhelmingly about the second.
Can herbs really interfere with chemotherapy?
Yes. St John's wort induces the liver enzyme CYP3A4, which many cancer drugs depend on. In a small crossover study of five patients, it lowered levels of irinotecan's active metabolite by 42% — meaning less drug reaching the cancer. NCCIH lists it as weakening some cancer medications.
Are supplements checked for safety before they are sold?
Not in the way medicines are. FDA states it does not have the authority to approve dietary supplements before they are marketed. FDA says a firm generally does not have to give it the evidence for safety before or after marketing a supplement.
Does that mean acupuncture, yoga and herbal tea are all off-limits?
No. NCCIH says some approaches, such as acupuncture, mindfulness-based stress reduction, and yoga, may help manage cancer symptoms and side effects of treatment. The question is whether something replaces treatment or interacts with it. That is answerable — bring the actual bottle or the practitioner's name to your team.
My reasons for distrusting conventional medicine are personal. Does that count?
It does, and it is worth saying out loud to your team. Cost, past mistreatment, faith, and bad experiences are real reasons people look elsewhere. None of them change what a herb does to a drug level — but they do change what a good conversation with your team needs to cover.
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Written by: Cancer ExplainedSources last checked: 2026-08-13 what this meansLast updated: 2026-10-01Next planned review: 2027-01-30
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Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes, and this is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
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How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes, and this is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and then compared with the sources listed on it, looking for statements those sources do not back up. That check is not a sentence-by-sentence record and can miss errors. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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