California Prop 65 for supplements: heavy-metal warnings explained

For any brand selling supplements into California, three words carry outsized weight: Proposition 65. The warning label, the lawsuits, the heavy-metal limits — Prop 65 is one of the most feared compliance topics in the US supplement world, and much of the fear comes from misunderstanding how it works. Here is what it actually requires.

What Prop 65 is

Proposition 65 is a California law that requires businesses to provide a clear and reasonable warning before exposing people to chemicals the state has identified as causing cancer or reproductive harm. The state maintains a list of these chemicals, which is updated over time.

It applies to products sold in California regardless of where they are made — so it reaches far beyond California-based companies. If you sell into the state, Prop 65 can apply to you.

Why supplements are in the firing line

Supplements are particularly exposed because of one category in particular: heavy metals. Elements such as lead, cadmium, arsenic, and mercury appear on the Prop 65 list, and they can occur as natural contaminants in botanical ingredients, minerals, and other raw materials — not because anyone added them, but because they are present in the source.

That makes supplements, especially those with botanical or mineral ingredients, a frequent target for Prop 65 attention.

The warning — and the safe harbor

The headline obligation is the warning: if a product can expose a consumer to a listed chemical above the relevant level, a warning is required. But there is important nuance. Prop 65 sets exposure levels below which a warning is generally not required — the so-called safe harbor levels. If exposure from the product is below the relevant level, the warning may not be needed.

This is why blanket warnings are not the only answer, and why knowing the actual contaminant levels in your product matters: it determines whether you are above or below the threshold that triggers a warning.

The enforcement reality

Much of Prop 65's fearsome reputation comes from its enforcement mechanism, which allows private actions against non-compliant products. This has produced a steady stream of actions in the supplement space, often centred on heavy metals. The practical consequence is that Prop 65 compliance is not theoretical — it is actively policed, and getting it wrong has real cost.

Because Prop 65 listings, levels, and warning requirements are detailed and change over time, confirm the current requirements for your specific product rather than relying on a general summary.

It comes back to the ingredients

The thread through all of this is ingredient data. Whether a product triggers a Prop 65 concern depends on the contaminant levels in its ingredients and the resulting exposure. Botanicals and minerals carry contaminant profiles; the finished product's exposure is the sum of what the ingredients contribute.

Knowing the contaminant data for your ingredients — and how it rolls up into the finished product — is what lets you assess Prop 65 exposure rather than guess at it.

Tracking contaminants from the formula

The robust approach is to hold contaminant data as part of each ingredient's record, so the heavy-metal picture of a formula can be assessed as it is built. When the ingredients carry their contaminant profiles, the finished product's exposure can be understood against the relevant thresholds — turning Prop 65 from a vague dread into a data question you can actually answer.

The takeaway

Prop 65 requires warnings for exposures to listed chemicals above safe-harbor levels, applies to anything sold in California, and hits supplements hardest through heavy-metal contaminants in botanical and mineral ingredients. It is actively enforced. Managing it well means knowing the contaminant data of your ingredients and how it rolls up — so you can tell whether a warning is genuinely required, rather than defaulting to fear.

Lemoniq holds contaminant data with each ingredient and rolls it up across the formula, so the heavy-metal exposure behind a Prop 65 assessment is visible as you build the product. We solve this exact problem. See how it works