Prop 65 for Supplement Brands: Lead, Safe Harbor Levels, Warnings and Amazon

Proposition 65, formally the Safe Drinking Water and Toxic Enforcement Act of 1986, is a law California voters approved in November 1986, 63 percent to 37 percent. It requires businesses to warn Californians about significant exposures to chemicals that cause cancer, birth defects or other reproductive harm (OEHHA: About Proposition 65). The Office of Environmental Health Hazard Assessment (OEHHA) runs the program and keeps the list, which it says has grown to roughly 900 chemicals and must be updated at least once a year.

The law is a right-to-know rule, not a safety ban. The California Attorney General's FAQ says a Prop 65 warning is not a regulatory decision that a product is safe or unsafe (California AG: Prop 65 FAQ). You can legally sell a supplement that needs a warning. What you cannot do is sell it to Californians without one.

Supplements are squarely covered. The warning regulations define food to include dietary supplements (27 CCR 25600.1(g)), and the food warning rules name dietary supplements directly. Location does not help either: the AG's FAQ says out-of-state manufacturers are not exempt if their products expose people in California. If you ship to California through Amazon, your own store or TikTok Shop, Prop 65 applies to you.

The chemical that matters most for supplement brands is lead. It occurs naturally in soil and is taken up by crops, as the AG's FAQ notes, so botanicals, minerals and plant proteins can carry it even when nobody added it. For the federal label rules that sit alongside Prop 65, see our supplement label requirements guide.

Labs report metals as a concentration, usually micrograms per gram (the same as parts per million). Prop 65 levels are per day. BSCG lays out the conversion: daily exposure equals the concentration times the grams per serving times the maximum servings per day on your label (BSCG: Heavy metals in supplements). Two of its worked examples show why format matters more than the raw number.

Botanical capsule: lead at 0.4 micrograms per gram, 0.5 grams of fill, two capsules a day. That is 0.4 times 0.5 times 2, or 0.4 micrograms a day, under the 0.5 MADL. Protein powder: lead at 0.05 micrograms per gram, a 30-gram scoop, two scoops a day. That is 0.05 times 30 times 2, or 3.0 micrograms a day: eight times lower in concentration than the capsule, yet six times over the MADL. Big servings turn small concentrations into big exposures, which is why our powder supplement launch guide treats heavy metals as a first-week question.

BSCG also flags a trap in how results are reported. A certificate of analysis that says lead is below 1 ppm tells you almost nothing for a powder: at 30 grams twice a day, that limit of quantitation (LOQ, the smallest amount the method can reliably measure) allows anything up to 60 micrograms a day. Ask the lab for an LOQ low enough that, multiplied by your daily serving mass, it falls under 0.5 micrograms. Our certificate of analysis guide walks through reading the rest of the report.

Amazon's California Proposition 65 help page puts the job on the seller. For every new and existing listing, you must decide whether the product needs a warning and give Amazon the correct warning through the listing itself, not by email or any other route. If you are reselling, you pass along the warning you received from the manufacturer. Amazon also says not to send labels, shelf signs or tags unless it instructs you to in writing.

Two details trip up small brands. First, Amazon says you are responsible for adding a warning even if you have fewer than 10 employees. That matters because Prop 65 itself exempts businesses with nine or fewer employees, as the AG's FAQ confirms. On Amazon, the small-business exemption does not get you out of the listing requirement. Second, Amazon says you are responsible even if someone else sells the same product.

Prop 65 is enforced through civil lawsuits. The AG's FAQ says the Attorney General, district attorneys and city attorneys in cities over 750,000 people can sue, and private parties acting in the public interest can sue too, but only after giving the business, the Attorney General and local prosecutors at least 60 days notice and only if no public prosecutor has acted. Courts can order a business to stop the violation, and penalties can reach $2,500 per violation per day. Warning requirements take effect 12 months after a chemical is added to the list.

If a 60-day notice arrives, the AG's FAQ suggests considering defense counsel, contacting the party that sent it to understand the claim and ask for its test data, running your own lab testing or exposure assessment, and, if the claim looks valid, stopping sales, telling retailers, recalling, or adding proper warnings. The AG's office says it cannot give private parties legal advice. Neither can we.