Heavy Metals, Pesticides and Microbes in Herbal Products
What surveys and reviews found about lead and other metals, pesticide residues, molds and microbes in herbal products, with the limits of each study and where evidence is missing.
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.
The question: how often are herbal products contaminated?
There is no single number. The studies we read looked at different products, in different countries and years, using different limits, and they are not a sample of the whole market. They show that contamination has been found in some products, not how likely it is in the one you hold. US rules say manufacturers are required to make sure supplements do not contain contaminants or impurities, [1] and the FDA states it does not test supplements before they are sold. [2]What the studies found
| Contaminant | What the source found | Limits |
|---|---|---|
| Lead, mercury, arsenic | 193 Ayurvedic medicines bought online in 2005 were analyzed; about one-fifth of both US-made and Indian-made products contained detectable lead, mercury or arsenic. [3] All metal-containing products exceeded at least one standard for acceptable daily intake of toxic metals. [3] | Specific category of traditional medicines; 2005 purchases |
| Metals and one traditional practice | The same authors note metals may be present because of the practice of rasa shastra, combining herbs with metals, minerals and gems. [3] Medicines made that way had metals more often (40.6% versus 17.1%). [3] | Describes one traditional practice; most herbal products do not use it |
| Metals, microbes, molds (many products) | A systematic review of 91 articles from 28 countries on herbal medicinal products in low- and middle-income countries found about 16.4% of samples above regulatory limits. [4] Microbial contamination exceeded limits most often (46.4%), then mycotoxins (25.8%), then metals (14.3%). [4] | Countries and limits differ; not US supplements |
| Pesticides, mycotoxins, microbes | In 26 milk thistle supplements from the US and Czech markets (2016-2017), large numbers of mycotoxins and several pesticides were detected, along with substantial microbiological contamination. [5] NCCIH reports the same concern for milk thistle products. [6] | One herb; small sample |
| Pesticide residues in Chinese medicines | A 2019 review in Chinese summarizes pesticide residue findings and detection methods for traditional Chinese medicines. [7] | We read only the English abstract; it gives no figures |
Mycotoxins are harmful substances produced by molds or other fungi, as NCCIH describes. [6]
What "above the limit" means
The review above counted samples over the regulatory limits used in each study. [4] Those limits are set by authorities and differ between countries, so a percentage from one study cannot be applied to a product from another market. A label claim of "Good Manufacturing Practices" was no guarantee in the Ayurvedic study: of the products with metals, 75% claimed it. [3]Frequently asked questions
Do herbal supplements contain lead?
Some do. A study of 193 Ayurvedic medicines bought online found detectable lead, mercury or arsenic in about one-fifth. [3] We did not find a current survey that covers herbal supplements in general.
Are organic herbal products free of pesticides?
We did not read a source that answers this. See organic labels and pesticide residues in herbal tea for the tea-specific page.
What are mycotoxins?
NCCIH describes them as harmful substances produced by molds or other fungi, and says some milk thistle products were contaminated with them. [6]
Does a "Good Manufacturing Practices" claim mean no contaminants?
Not in the one study we read: 75% of the metal-containing Ayurvedic products claimed it. [3]
Who should be most careful?
The sources we read for this page do not rank groups. NCCIH notes many supplements have not been tested in pregnant women, nursing mothers or children. [1] Ask a clinician.
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
Limits and uncertainty
Proper evidence not found: in the sources we read we did not find a current, nationwide survey of heavy metals, pesticide residues or microbes in herbal supplements sold in the US that covers many herbs. We searched PubMed for heavy metal contamination in herbal supplements, pesticide residues in botanical supplements and microbial contamination of herbal products. The results above are what we could read. For the safety-library overview see heavy metals in supplements and herbal products and product quality and contamination.
Related: herbal tea heavy metals and the quality overview.
Safety and who should ask
- What a reader can do. Check the label for the plant name and part, and the manufacturer's contact details; the FDA says labels must give an address or phone number for reporting serious adverse events. [2] Ask a pharmacist or clinician about any product, especially if you are pregnant or breastfeeding, give products to children, or have liver or kidney disease.
- If you feel unwell. Tell your clinician which products you used and bring the package. See side effects and reporting. If poisoning is possible, call Poison Help at 1-800-222-1222 in the US; for an emergency call 911.
- Hidden ingredients. Contamination is not the only way contents differ from the label: the FDA has found prescription drugs in products sold as supplements. [1]
We do not describe home tests for contamination, because we found no source for them.
References
- National Center for Complementary and Integrative Health (NIH, US). Using Dietary Supplements Wisely. Page last updated January 2019. Read 2026-10-23.
- U.S. Food and Drug Administration. Questions and Answers on Dietary Supplements. Content current as of 27 August 2026. Read 2026-10-23.
- Saper RB, Phillips RS, Sehgal A, et al. Lead, mercury, and arsenic in US- and Indian-manufactured Ayurvedic medicines sold via the Internet. JAMA. 2008;300(8):915-923. PMID 18728265. Read 2026-10-23.
- Opuni KFM, Kretchy JP, Agyabeng K, et al. Contamination of herbal medicinal products in low-and-middle-income countries: A systematic review. Heliyon. 2023;9(9):e19370. PMID 37674839. Read 2026-10-23.
- Fenclova M, Novakova A, Viktorova J, et al. Poor chemical and microbiological quality of the commercial milk thistle-based dietary supplements may account for their reported unsatisfactory and non-reproducible clinical outcomes. Scientific Reports. 2019;9:11118. PMID 31366891. Read 2026-10-23.
- National Center for Complementary and Integrative Health (NIH, US). Milk Thistle: Usefulness and Safety. Page last updated February 2025. Read 2026-10-23.
- Li HJ, Zhang WS, Wu JS, Xin WF. Research progress of pesticide residues in traditional Chinese medicines (article in Chinese; English abstract read). Zhongguo Zhong Yao Za Zhi. 2019;44(1):48-52. PMID 30868811. Read 2026-10-23.
Education, not medical advice. This page is for general information. It does not diagnose or treat any condition and is not a substitute for care from a qualified health professional. Natural does not automatically mean safe. Ask a clinician or pharmacist before changing your care, especially if you take medication, are pregnant or breastfeeding, or have a health condition.