Adulteration and Substitution of Herbs: What DNA Studies and Regulators Found
Studies and regulators describe herbal products that hold other plants, fillers, dyes or hidden drugs. See what was found, why the numbers differ and what the tests cannot show.
Content last updated . This page has not been medically reviewed.
Safety first. Supplements can cause side effects and interact with medicines. Read mushroom safety and interactions before you use any mushroom product.
Safety first: when a substitute is poisonous
Most of this page is about how often herbal products are not what the label says. The most serious cases are products that hold a toxic plant. In an FDA alert, products labeled as tejocote (Crataegus mexicana) root or Brazil seed were found to contain yellow oleander (Thevetia peruviana) instead, and FDA says this plant can cause nervous system, stomach and bowel, and heart effects that may be severe or even fatal. [1] FDA advises people not to use the products on its alert, and to contact a health care provider even if they stopped using them some time ago. [1]
If someone feels seriously unwell after taking any product, call 911 (US). For poisoning advice in the US, call Poison Help at 1-800-222-1222. For other countries see poison help by country.
What "adulteration" means
A herbal product is adulterated when it is not what it claims to be. One review describes adulteration as including contamination, use of fillers and product substitution, and says it can be accidental or deliberate. [2] In the United States, firms are prohibited from marketing dietary supplements that are adulterated or misbranded. [3]
The label can also leave things out. NCCIH (part of the US National Institutes of Health) reports that FDA has found prescription drugs, including the anticoagulant warfarin and the anticonvulsant phenytoin, in products sold as dietary supplements. [4]
What studies found
These figures describe samples that researchers bought and tested. They are not the chance that your bottle is affected.
| Question | What the source found | Strength of evidence | What was tested |
|---|---|---|---|
| How common is it worldwide? | A survey of published DNA-testing reports found 27% of the products were adulterated against their labeled species, and the rate differed a lot between continents. [2] | Mixed: it pools reports that used different tests and markets | 5,957 herbal products in 37 countries, DNA-based methods [2] |
| Turmeric (Curcuma longa) | A review of published reports found an overall rate of 20.0%, with spice at 20.4% and supplements at 22.0%. [5] Reported problems include undeclared dyes such as lead chromate and metanil yellow. [5] | Mixed: shows a repeating problem, not a rate for any one product | 2,235 commercial samples from 48 publications [5] |
| Ginseng (Panax species) | 24% of products were reported as adulterated, usually with another Panax species. [6] Replacing the root with leaves, stems or flowers was also reported. [6] | Mixed: rates differed by continent and country | 507 products in 12 countries [6] |
| Toxic substitutes | FDA laboratory work found yellow oleander in products labeled as tejocote root or Brazil seed. [1] | Documented for the products FDA named; not a rate | Products FDA tested [1] |
The ginseng review says price differences of tenfold or more between processed types are the main driver of intentional adulteration. [6]
A widely cited study that was retracted
A 2013 study in BMC Medicine used DNA barcoding on 44 herbal products sold in the USA and Canada. The 2019 survey above discusses it. [2] In 2024 the journal retracted it. The editor wrote that a University of Guelph investigation found evidence of data fabrication; the original authors disagree with the retraction. [7] We do not use that study's figures. Because the 2019 survey discusses it, treat pooled percentages as a rough sign of a real problem, not as exact rates.
What the tests cannot tell you
- Different methods give different answers. The share of products found adulterated varies to some extent with the DNA method used. [2]
- Processing can erase the clue. False negatives can be expected when DNA is degraded or lost during processing or manufacturing. [2] A mini-review of DNA methods lists harvesting, drying, storage and processing as causes of degraded DNA, and also lists contamination and database errors as causes of false positives. [8]
- Studies sample narrow slices. The investigations are limited to particular regions, markets, product types or plants. [2]
- Proper evidence not found for a reliable, current adulteration rate for the herbal products sold in any one country. We looked in the reviews above and the FDA pages we read; they give pooled or sample-based figures only.
What regulators say
FDA says it is not authorized to approve dietary supplements for safety and effectiveness before they are marketed. [9] It can act against adulterated or misbranded supplements only after the product is on the market, and it says it cannot test every product that may have hidden ingredients. [4] FDA also says its limited resources go first to public health emergencies and products that may have caused injury. [10] Rules in other countries differ; the sources we read for this page do not describe them.
What a reader can do
- Ask a pharmacist or clinician before using a herbal product, especially with prescription medicines, pregnancy or breastfeeding, a child, liver or kidney disease, or planned surgery. A hidden ingredient cannot be judged from the label. See how interactions work.
- Learn what a good label shows in reading an herbal supplement label and what testing can and cannot show in third-party testing for herbal products.
- Report a problem with a product. See side effects and reporting.
Related reading: product quality and contamination, heavy metals, pesticides and microbes, unsafe products and warnings, adaptogen product adulteration and herbal tea adulteration, mold and mislabeling.
Frequently asked questions
How common are adulterated herbal products?
A survey that pooled DNA-testing reports from 37 countries found 27% of 5,957 products adulterated, with large differences between continents. [2] Those studies tested different products and used different methods, so the figure is a rough sign, not a rate for any one product.
Can a DNA test prove my supplement is pure?
No. DNA tests look for plant DNA, and processing can degrade it, which can cause false negatives. [2] Contamination and database errors can cause false positives. [8]
What happened to the 2013 study that found many products contained other plants?
The journal retracted it in 2024 after a university investigation found evidence of data fabrication. The original authors disagree with the retraction. [7]
Does "natural" or "organic" on the label mean a product is not adulterated?
NCCIH says "natural" does not always mean safer or better, and that an herbal supplement may contain many compounds that are not all known. [11] See organic, wildcrafted and sustainably harvested herbs for what organic labels cover.
What should I do if I think a product is not what the label says?
For products named in an FDA alert, FDA advises consumers to stop using and dispose of them. [1] For anything else, ask a pharmacist or clinician whether to keep using it, and do not change a prescribed medicine without asking the prescriber or pharmacist.
References
- US Food and Drug Administration. FDA Issues Warning About Certain Products Containing Toxic Yellow Oleander (page updated September 2026). Read 2026-10-23.
- Ichim MC. The DNA-Based Authentication of Commercial Herbal Products Reveals Their Globally Widespread Adulteration. Front Pharmacol 2019. Read 2026-10-23.
- US Food and Drug Administration. Dietary Supplements. Read 2026-10-23.
- NCCIH (US). Using Dietary Supplements Wisely. Read 2026-10-23.
- Gafner S, Orhan N, Kahraman C, Blumenthal M. A scoping review of turmeric adulteration based on data from six continents. Pharm Biol 2026. Read 2026-10-23.
- Ichim MC, de Boer HJ. A Review of Authenticity and Authentication of Commercial Ginseng Herbal Medicines and Food Supplements. Front Pharmacol 2020. Read 2026-10-23.
- BMC Medicine Editorial Office. Retraction Note: DNA barcoding detects contamination and substitution in North American herbal products. BMC Med 2024. Read 2026-10-23.
- Raclariu-Manolică AC, Mauvisseau Q, de Boer HJ. Horizon scan of DNA-based methods for quality control and monitoring of herbal preparations. Front Pharmacol 2023 (mini review). Read 2026-10-23.
- US Food and Drug Administration. Information for Consumers on Using Dietary Supplements. Read 2026-10-23.
- US Food and Drug Administration. Questions and Answers on Dietary Supplements. Read 2026-10-23.
- NCCIH (US). Natural Doesn't Necessarily Mean Safer, or Better. Read 2026-10-23.