Does Your Mushroom Coffee Contain Lead? Three Brands Have Been Caught

Mushrooms are nature's filters. They are bioaccumulators — organisms that concentrate substances from their environment into their tissues. In the wild, this is how mushrooms acquire trace minerals from soil. In the supplement industry, this is also how they acquire lead, cadmium, arsenic, and mercury when they are grown on contaminated substrate or in contaminated soil and water.

This is well known to mushroom industry chemists. It is the reason any reputable mushroom brand tests for heavy metals on every batch and publishes the Certificate of Analysis. It is also the reason that, of the major mushroom coffee brands sold in the United States in 2026, the two largest have both been the subject of Proposition 65 lead settlements — and the largest of all does not publish a single heavy metals test result.

Why mushrooms accumulate heavy metals

Heavy metals are naturally present in soil, water, and substrate materials at varying concentrations. Mushrooms, in the process of metabolizing nutrients from their growing environment, also pull in these contaminants and concentrate them in their fruiting body or mycelium. The concentration factor depends on the species, the substrate, the growing conditions, and the part of the mushroom analyzed.

The four heavy metals that matter most for mushroom supplements are:

• Lead — neurotoxic, no known safe level of exposure. California's Prop 65 safe-harbor level is 0.5 micrograms per day.
• Cadmium — kidney toxin, classified as a known human carcinogen by the EPA. California's Prop 65 safe-harbor is 4.1 micrograms per day.
• Arsenic (inorganic) — carcinogen and developmental toxin. California's Prop 65 safe-harbor is 10 micrograms per day.
• Mercury — neurotoxin, especially for developing nervous systems. Limited Prop 65 enforcement on supplements.

California's Proposition 65 is the most aggressive consumer-protection regime in the United States for heavy metals in food and supplements. Any product that exposes a consumer to more than the safe-harbor level per day must carry a warning. Failure to provide the warning is a violation that can be enforced by the state Attorney General or by private citizens through 60-day notice and lawsuit. Both routes have been used aggressively against mushroom products in recent years.

RYZE: $20,500 settlement (2024)

On August 22, 2024, Environmental Health Advocates, Inc. — a Prop 65 enforcement organization — served RYZE Superfoods with a 60-Day Notice of Violation. The notice alleged that RYZE Mushroom Overnight Oats contained lead, and that consumers were not being given the Prop 65 warnings California law requires.

The settlement was filed with the California Department of Justice. RYZE paid $20,500 to the claimant and its counsel. RYZE also agreed not to sell any product in California that exposes a person to more than 0.5 micrograms of lead per serving per day without a Prop 65 warning. The 0.5 microgram figure is California's safe-harbor level — the threshold above which warnings become mandatory. RYZE settled exactly at that line.

RYZE now hosts a Prop 65 page on its website acknowledging that some ingredients "may contain naturally occurring lead" and that "chemicals known to the State of California to cause cancer or reproductive harm may be present." That page exists because of this settlement.

RYZE does not publish heavy metals test results for its products. There is no Certificate of Analysis available on the RYZE website. There is no batch-level testing data. There is the Prop 65 page, the settlement document, and the brand's continued marketing of itself as a wellness product. For a brand that has settled a lead contamination case, the absence of transparency around testing is a meaningful red flag.

Four Sigmatic: 2018 Prop 65 notice + 2024 independent testing

Four Sigmatic, the original major mushroom coffee brand, has its own lead history. We are calling it out because we are trying to be honest about the category, not just about RYZE.

In 2018, Four Sigmatic was served with a Prop 65 Notice of Violation alleging their products contained lead at levels requiring California consumer warnings. The notice is on file with the California DOJ. We were not able to find a published settlement document, which suggests the case was either settled privately, dropped, or resolved through a label change.

In August 2024, independent testing by Lead Safe Mama LLC — a long-running consumer testing project run by Tamara Rubin — found that Four Sigmatic Think Organic Coffee tested positive for lead. The exact ppb values were documented in a lab report but were not publicly disclosed in Lead Safe Mama's public summary. Rubin noted, in her standard framing on this kind of result: "there is no safe level of Lead exposure." Four Sigmatic has not publicly responded to the 2024 testing as far as we have been able to find.

Four Sigmatic, unlike RYZE, has historically claimed to test for heavy metals — though COAs are not easily accessible from the brand's website. "We test" is not the same as "here is the test result." The 2024 Lead Safe Mama finding suggests that internal testing, if it is happening, is not catching everything an independent third party can find.

ConsumerLab's testing on Host Defense

Host Defense — Paul Stamets' mushroom supplement brand and the original mycelium-on-grain pioneer — is not a mushroom coffee brand, but it shows up in the same supplement aisles and the same heavy metals testing. ConsumerLab tested 12 lion's mane and chaga supplements, including mushroom coffees and capsules, and found that Host Defense products showed arsenic, lead, and cadmium above ConsumerLab's "Action Levels."

ConsumerLab also found that one mushroom coffee powder it tested contained much less beta-glucan than expected from its label, and that four lion's mane products could not be approved because they were labeled as containing "mushroom" despite being made from mycelium — a labeling violation per ConsumerLab's standards. Of the 12 products tested, ConsumerLab named Real Mushrooms as the "Best Mushroom Supplement Company" based on high beta-glucan levels, nonexistent contaminant levels, and no grain content.

Stamets has disputed the testing methodology and argued that standard assays miss insoluble beta-glucans in mycelium. We are not in a position to settle that debate. What we can report is that the only independent third-party testing organization with a paid review of mushroom supplements found heavy metals above its action levels in Host Defense products.

Why this is a category-wide problem

Prop 65 enforcement against mushroom products has been increasing. A March 2025 Notice of Violation was served on Borde SA and Costco for dried porcini mushrooms containing lead and cadmium. Prop 65 cases targeting heavy metals in supplements, spices, mushrooms, and herbal powders have spiked since the pandemic, with rising settlement amounts.

Approximately 85% of the world's functional mushrooms are grown in China, with major production clusters in Guangdong, Jiangsu, and Henan provinces. Chinese soil and water testing standards are generally less rigorous than U.S. or EU standards, and supply chains are less transparent. This is not an indictment of all Chinese-grown mushrooms — Real Mushrooms sources from China and publishes COAs that are among the cleanest in the industry, because they spend the testing budget. It is, however, a reason that any mushroom brand selling at scale in 2026 needs to be testing for heavy metals on every batch and publishing the result.

The brands that do this well — Real Mushrooms is the standard-bearer — make heavy metals testing data available within 24 hours of any consumer request, and most publish recent COAs directly on their websites. The brands that do not, and that have nonetheless been caught with lead, are the ones consumers should be most cautious about.

How to evaluate a mushroom coffee for heavy metals

Three checks before you buy:

1. Does the brand publish a Certificate of Analysis showing heavy metals testing? Look for lead, cadmium, arsenic, and mercury values, ideally in micrograms per serving so you can compare to Prop 65 safe-harbor levels (0.5 mcg lead, 4.1 mcg cadmium, 10 mcg inorganic arsenic). If you cannot find a COA on the brand's website, email them and ask. A brand that takes 24 hours to send one is fine. A brand that cannot produce one at all is a problem.
2. Has the brand been the subject of a Prop 65 notice or settlement? Search the California Attorney General's Prop 65 settlement database for the brand name. RYZE and Four Sigmatic both appear there. The presence of a notice is not by itself disqualifying — many large food companies have Prop 65 history — but it raises the bar on what testing transparency should look like going forward.
3. Does the brand carry a Prop 65 warning page or label? RYZE's existence of a Prop 65 disclaimer page is itself a piece of public information. Brands that have crossed the safe-harbor threshold and disclose it are at least disclosing. Brands that have crossed the threshold and have not been caught are the harder problem.

Mushrooms are not unsafe to consume. Functional mushrooms have been part of traditional medicine for thousands of years and clinical studies routinely use them at much higher doses than mushroom coffee delivers. The question is not whether mushrooms are safe — it is whether the specific batch in your specific bag has been tested by anyone, and whether the brand selling it is willing to show you the result. In 2026, that is a much shorter list than the marketing pages suggest.