What chemicals does Prop 65 cover for dietary supplements?

The chemicals most relevant to supplements are heavy metals: lead, cadmium, arsenic, and mercury. Lead has a Maximum Allowable Dose Level (MADL) of 0.5 micrograms per day for reproductive harm and a cancer No Significant Risk Level (NSRL) of 15 micrograms per day. Warnings are triggered at whichever threshold is lower. Other chemicals on the Prop 65 list that may appear in supplements include certain herbal extracts, solvents used in processing, and naturally occurring compounds in botanical ingredients. The full list maintained by OEHHA carried 879 entries as of July 31, 2026; OEHHA describes it as roughly 900 chemicals.

What does a Prop 65 warning label look like?

Prop 65 requires a clear and reasonable warning when a warning is required. OEHHA provides safe-harbor formats, including a food format that expressly covers dietary supplements. The full-length food warning uses a bold uppercase signal word (WARNING, CA WARNING, or CALIFORNIA WARNING), identifies the relevant chemical and harm, and links to www.P65Warnings.ca.gov/food. Its wording begins with consuming the product; the food format does not require a warning symbol. The short-form rules also have a food option. Products manufactured and labeled before January 1, 2028, may continue using the prior short-form content under the transition rule, regardless of when they are sold. Use OEHHA's applicable format and methods for the exposure being warned about.

California Prop 65 for Supplement Brands: What You Need to Know

Q: Does Prop 65 apply to supplement brands outside California?

Yes, in most cases. Prop 65 is not limited to California companies: if a non-exempt business sells products to California consumers (online, through Amazon or Walmart, or through any national retailer), its warning duties apply regardless of where the company is located. Two exemptions matter: businesses with fewer than 10 employees are exempt from the warning requirement, and no warning is required when exposure is low enough to fall below OEHHA's safe-harbor levels (the exposure-based exemption brands rely on through testing). Most major retailers and marketplaces separately require Prop 65 compliance as a condition of doing business.

Last reviewed: April 1, 2026 | Next review: October 1, 2026

By Greg Huang, founder since 2009 in the dietary supplement and nutrition industry

Reviewed by Dr. James Pendleton, ND, licensed primary care physician, 20+ years in naturopathic medicine

Proposition 65 (officially the Safe Drinking Water and Toxic Enforcement Act of 1986) is California's chemical warning law. It requires businesses to warn consumers about significant exposures to chemicals that cause cancer, birth defects, or reproductive harm.

For supplement brands, Prop 65 is the single most common source of private lawsuits. Plaintiffs (often called "bounty hunters") can sue any business that sells a product containing a listed chemical without providing a warning. Settlements typically range from $25,000 to $100,000+ (based on California Attorney General annual settlement reports, Perkins Coie litigation analysis, and Spencer Fane 2026 data). The law reaches every non-exempt brand that sells to California consumers, regardless of where the brand is based. The exemptions are narrow: businesses with fewer than 10 employees are exempt from the warning requirement, and exposures below OEHHA's safe-harbor thresholds do not require a warning.

The short answer

Prop 65 applies to products sold to California consumers regardless of where the brand is based, unless an exemption applies: businesses with fewer than 10 employees are exempt, and exposures below safe-harbor thresholds need no warning. The chemicals most relevant to supplements are heavy metals: lead, cadmium, arsenic, and mercury. Lead's threshold is 0.5 micrograms per day.

Dietary supplement manufacturers must comply with 21 CFR Part 111 (Current Good Manufacturing Practice for dietary supplements). This includes requirements for personnel, facilities, equipment, production, laboratory operations, and record-keeping.

Key Takeaways

Prop 65 applies to products sold to California consumers regardless of where the brand is based, unless an exemption applies: businesses with fewer than 10 employees are exempt, and exposures below safe-harbor thresholds need no warning.
The chemicals most relevant to supplements are heavy metals: lead, cadmium, arsenic, and mercury. Lead's threshold is 0.5 micrograms per day.
You have two compliance options: test and confirm levels below safe harbor thresholds, or add a Prop 65 warning label to your product.
Prop 65 lets any individual acting in the public interest sue an alleged violator, alongside the Attorney General, district attorneys, and larger cities. In our assessment, that private enforcement (not government action) is what drives most compliance cost for supplement brands, and prevention is cheaper than settlement.

What Prop 65 Is

Prop 65 maintains a list of roughly 900 chemicals known to the State of California to cause cancer, birth defects, or reproductive harm. The list published July 31, 2026 carries 879 entries. It is updated regularly by the Office of Environmental Health Hazard Assessment (OEHHA).

The law has two provisions. First, businesses may not knowingly discharge listed chemicals into drinking water sources. Second, businesses must provide a "clear and reasonable" warning before exposing anyone to a listed chemical. The second provision is the one that affects supplement brands.

Prop 65 does not ban products or set product standards. It requires warnings. A product with lead above the safe harbor level is legal to sell, as long as it carries a Prop 65 warning. A product without a warning that exposes consumers to a listed chemical above the threshold is a violation.

Why Prop 65 Matters Outside California

Many brand owners assume Prop 65 is a California-only issue. That assumption is wrong and expensive.

E-commerce reaches California. If you sell online and don't block California shipments (almost nobody does), Prop 65 applies. Amazon, Shopify, and every major e-commerce platform ship to California by default.
National retailers require compliance. Major retailers including Amazon and Walmart require Prop 65 compliance in their agreements with brands. Most large retailers operating in California include similar requirements.
Plaintiff attorneys monitor nationally. Prop 65 bounty hunter firms test products purchased from anywhere that ships to California. They don't care where your company is based. They care whether your product contains listed chemicals without a warning.
Other states are watching. Several states have proposed or enacted similar chemical warning laws. Building Prop 65 compliance into your process now prepares you for future regulations.

Chemicals Most Relevant to Supplements

Of the 900+ chemicals on the Prop 65 list, a handful appear regularly in dietary supplement testing. Heavy metals are the primary concern because they occur naturally in soil, water, and plant-based ingredients.

Chemical	Why It Appears in Supplements	Prop 65 Concern
Lead	Present in soil, absorbed by plants. Found in many botanical ingredients, calcium from natural sources, and some protein powders.	Cancer and reproductive harm. MADL: 0.5 mcg/day (reproductive). NSRL: 15 mcg/day oral (cancer).
Cadmium	Occurs in soil and is absorbed by root vegetables and grains. Found in cocoa-based products and some protein powders.	Cancer and reproductive harm. MADL: 4.1 mcg/day oral (reproductive). NSRL: 0.05 mcg/day inhalation (cancer).
Arsenic (inorganic)	Found in rice-based products, some seaweed ingredients, and groundwater-irrigated botanicals.	Cancer. NSRL: 10 mcg/day except inhalation; 0.06 mcg/day inhalation.
Mercury	Primarily a concern in fish oil and marine-derived ingredients.	Developmental harm (mercury and mercury compounds listed July 1, 1990; methyl mercury listed July 1, 1987). Methylmercury compounds were listed for cancer May 1, 1996. No safe-harbor number: OEHHA has adopted no NSRL or MADL for either.

NSRL and MADL are daily exposure thresholds. NSRL (No Significant Risk Level) applies to carcinogens. MADL (Maximum Allowable Dose Level) applies to reproductive toxicants. Some chemicals, like lead and cadmium, have both an NSRL and a MADL. When both apply, warnings are triggered at whichever threshold is lower. These values are set by OEHHA and change periodically. Always check the current OEHHA list for the most recent threshold values.

Not every listed chemical has a safe-harbor number, and the absence of one is not an exemption. Mercury is the example on this page. OEHHA states that a business causing an exposure must provide a warning unless it can demonstrate that the anticipated exposure does not pose a significant risk of cancer or reproductive harm, and it recommends qualified professional review because that determination can be complex. See OEHHA's guidance for businesses. Where no safe harbor exists, “test and confirm you are below the threshold” is not available as a compliance path, because there is no threshold to test against.

Testing and Compliance Options

You have two paths to Prop 65 compliance. Most brands use a combination of both, depending on the product and the specific chemicals involved.

Option 1: Test Below Safe Harbor Levels

Test your finished product for relevant Prop 65 chemicals. If levels are below the safe harbor thresholds (NSRL/MADL), no warning is required. This is the preferred approach because it avoids the consumer perception issues that come with a warning label.

Cost: $150 to $500 per test panel per batch (published lab pricing for a four-metal ICP-MS panel starts around $164 per sample; broader Prop 65 panels run higher)
Best for: Products where you can control ingredient sourcing and consistently achieve low levels
Risk: Natural variation in botanical ingredients means levels can change batch to batch

Option 2: Add a Prop 65 Warning Label

Apply a compliant Prop 65 warning to your product. This is simpler but has trade-offs. Some consumers avoid products with Prop 65 warnings. Some Amazon categories have higher return rates on warned products.

Cost: Minimal (label design and printing)
Best for: Products with naturally high levels of listed chemicals or ingredients with inconsistent sourcing
Risk: Consumer perception, potential competitive disadvantage

For guidance on what testing to expect from your manufacturer, see our supplement testing requirements guide. For understanding test results, see our guide to reading a COA.

Warning Label Requirements

OEHHA's safe-harbor regulations provide warning formats and methods deemed clear and reasonable. These formats are optional: a business using an alternative may need to defend it if challenged. Food warnings, including dietary supplements, have specific content under 27 CCR 25607.2. Use the provisions for the relevant exposure.

What the Full-Length Food Warning Includes

WARNING, CA WARNING, or CALIFORNIA WARNING in bold uppercase
Food-specific wording about consuming the product; no warning symbol is required for this format
The relevant listed chemical names and cancer or reproductive-harm wording for the exposure
The food warning URL: www.P65Warnings.ca.gov/food
The applicable food-warning presentation and delivery requirements in 27 CCR 25607.1

Where the Warning Must Appear

Follow the applicable food-warning delivery methods in 27 CCR 25607.1. For internet sales, the safe-harbor rules also require an online warning before purchase is completed. The warning can appear on the product display page, through a clearly marked warning link on that page, or through another prominent display before checkout is completed. Purchasers must not have to search the general website content for it. The online warning does not replace the warning delivered on or with the product. See OEHHA's business FAQ.

Common Prop 65 Mistakes

Assuming it doesn't apply because you're not in California. Any product sold to California consumers is covered. Online sales count. National retail counts. If your product can reach California, Prop 65 applies.
Using an outdated warning format. The short-form transition depends on when a product was manufactured and labeled. Under 27 CCR 25603(c), products manufactured and labeled before January 1, 2028, may use the prior short-form content regardless of their sale date. Check the applicable food-warning format rather than assuming every older product must be relabeled by the end of 2027.
Testing only finished product and not raw materials. If your ingredients have high heavy metals before blending, the finished product will too. Test incoming raw materials to catch problems before production. This also gives you leverage with ingredient suppliers.
Not testing every batch. Natural ingredients vary. One batch of turmeric may have low lead. The next batch from a different growing region may not. Batch-level testing is the only way to know.
Ignoring e-commerce warning requirements. For internet purchases using the safe harbor, a physical warning alone is insufficient. Section 25602(b) also provides online methods: the warning on the product display page, a clearly marked warning link on that page, or another prominent warning before purchase is completed. Do not hide it in general website content.
Waiting for a lawsuit to take action. Prop 65 settlements average $25,000 to $100,000+ (Spencer Fane 2026 analysis). Annual testing costs $1,000 to $3,000 (industry estimate). The math favors prevention. Plaintiff firms specifically target brands without warnings.

Getting Started with Prop 65 Compliance

Prop 65 compliance does not require a lawyer for every step, but it does require a systematic approach.

Identify which Prop 65 chemicals are relevant to your product. Heavy metals are the default concern. Botanical ingredients may trigger additional chemicals on the list.
Add heavy metals testing to your finished product testing protocol. Request lead, cadmium, arsenic, and mercury on every COA.
Compare results against OEHHA safe harbor levels. Your calculation must account for the recommended daily serving size (exposure = concentration times serving size).
If levels are below safe harbor: document your testing and keep records. If levels are above: add a compliant Prop 65 warning to your label and e-commerce listings.
Review your ingredient sourcing. Brands that control ingredient quality upstream have an easier time staying below Prop 65 thresholds.
If you sell on Amazon, complete the Prop 65 fields in your product listing. Missing these fields can trigger listing deactivation.

For a broader view of compliance risks, see our supplement compliance risks guide. For label requirements beyond Prop 65, see our packaging and label compliance guide.

Get compliance help on Prop 65

Prop 65 decisions usually run through a regulatory consultant. Our directory covers independently assessed regulatory and compliance providers. Browse regulatory providers →

Greg Huang, founder since 2009 in the dietary supplement and nutrition industry

Founder of Inventory Ready. Previously founded and operated multiple consumer brands in the dietary supplement and nutrition industry since summer 2009.

Stay informed

Regulatory updates, new manufacturer assessments, and tool launches. No spam.

Disclaimer: This guide is educational content, not legal or regulatory advice. Prop 65 compliance involves legal obligations. Consult a qualified attorney experienced in Prop 65 litigation before finalizing your compliance approach. OEHHA thresholds and the Prop 65 chemical list are updated regularly. See our Terms of Service for details.

Primary sources

The sourced claims in this guide are grounded in the following primary references. The guide's source manifest maps each claim to its source and verification date.