On November 7, 2023, the US Court of Appeals for the Ninth Circuit held that California's Prop 65 warning for glyphosate—the active ingredient in the herbicide Roundup®—violates the First Amendment. The court determined that because the warning did not qualify as "purely factual and uncontroversial," it should be subject to the intermediate scrutiny standard used to review compelled commercial speech. Under that standard, the court acknowledged California's substantial interest in preserving the health of its citizens but held that "compelling sellers to warn consumers of a potential 'risk' never confirmed by any regulatory body—or of a hazard not 'known' to more than a small subset of the scientific community—does not directly advance that interest." The court also concluded that California has less burdensome ways to share any concerns it may have about glyphosate.

Prop 65

Proposition 65, which was approved by California voters in 1986, requires California to publish a list of chemicals known to cause cancer or birth defects or other reproductive harm. The list now includes more than 900 chemicals. Businesses subject to Prop 65 are required to provide a "clear and reasonable warning" if they knowingly and intentionally expose an individual in California to one or more of the listed chemicals, unless the exposure is low enough to cause no significant risk. Prop 65 is enforceable through civil penalties of up to $2,500 per violation per day, and cases filed by advocacy groups, law firms and other private citizens are common.

Prop 65 Warning for Glyphosate

Glyphosate is the active ingredient in the herbicide Roundup®. In 2015, the International Agency for Research on Cancer (IARC) identified glyphosate as "probably carcinogenic to humans." The US Environmental Protection Agency has disagreed, concluding that the available data does not support a finding that glyphosate is carcinogenic to humans. Other regulators around the world have likewise disagreed that glyphosate is carcinogenic. Based on the IARC report, California placed glyphosate on the Prop 65 list in 2017.

Legal Challenge to Prop 65

In 2018, the US District Court for the Eastern District of California granted a preliminary injunction against enforcement of the Prop 65 warning for glyphosate. After considering alternative warnings proposed by California during the litigation, the district court granted a permanent injunction in 2020, finding that the compelled warning violates the First Amendment as applied to glyphosate.

A divided panel of the Ninth Circuit affirmed. The majority explained that compelled commercial speech is normally subjected to intermediate scrutiny but that a lower standard applies to compelled disclosure of "purely factual and uncontroversial information." The majority held that the exception for purely factual and uncontroversial information did not apply to the glyphosate warning because the concept of a risk being "known" to California was misleading without knowledge of the scientific debate on the subject. The majority also held that it was controversial to label something as having serious health effects "without a strong scientific consensus" and that here, the IARC's assessment of glyphosate's risk "stands essentially alone."

WARNING: This product can expose you to glyphosate. The State of California has determined that glyphosate is known to cause cancer under Proposition 65 because the International Agency for Research on Cancer has classified it as a carcinogen, concluding that there is sufficient evidence of carcinogenicity from studies in experimental animals and limited evidence in humans, and that it is probably carcinogenic to humans. The EPA has concluded that glyphosate is not likely to be carcinogenic to humans. For more information about glyphosate and Proposition 65, see www.P65warnings.ca.gov.

But the majority concluded that even if "literally true," the warning must still receive intermediate scrutiny because it "elevates one side of a legitimately unresolved scientific debate."

The majority reached the same conclusion on a further rewritten warning that said:

Using this product can expose you to glyphosate. The International Agency for Research on Cancer classified glyphosate as probably carcinogenic to humans. US EPA has determined that glyphosate is not likely to be carcinogenic to humans; other authorities have made similar determinations. A wide variety of factors affect your potential risk, including the level and duration of exposure to the chemical. For more information, including ways to reduce your exposure, go to www.P65Warnings.ca.gov/glyphosate.

Because the majority concluded that the exception for "purely factual and uncontroversial information" did not apply, it proceeded to apply the intermediate scrutiny standard, which requires that the provision controlling speech "directly advance" a "substantial" governmental interest through means that are no "more extensive than necessary."

The majority held that all of the proposed Prop 65 warnings for glyphosate were unconstitutional under intermediate scrutiny. It acknowledged California's substantial interest in protecting its citizens but concluded that compelling businesses to warn of "a potential 'risk' never confirmed by any regulatory body" and "not 'known' to more than a small subset of the scientific community" does not "directly advance that interest." The majority also held that "California could employ various other means to promote its (minority) view that glyphosate puts humans at risk of cancer," such as posting "information about glyphosate on its own website or conduct[ing] an advertising campaign."

The dissent argued that the court should have remanded the case to the district court to review the rewritten Prop 65 warning in the first instance. California has until November 21, 2023, to seek rehearing en banc.


The debate over glyphosate is somewhat unusual in terms of the number of regulatory authorities that have disagreed with the IARC's assessment. But it is not unique. For example, the Personal Care Products Council (PCPC) is currently litigating a similar First Amendment challenge in the Eastern District of California to the listing of respirable, unbound particles of titanium dioxide, the toxicity of which is also the subject of considerable scientific dispute. The PCPC's motion for a preliminary injunction against California's enforcement of Prop 65 with respect to titanium dioxide is being briefed now. The Ninth Circuit's glyphosate decision will play heavily in the proceedings, and it is likely that the Ninth Circuit will ultimately be called on to review the district court's resolution of the PCPC litigation.

More broadly, the Ninth Circuit's decision is likely to make it harder for California to require Prop 65 warnings where there is robust scientific debate about whether a chemical causes cancer or birth defects or other reproductive harm.


WilmerHale's Energy, Environment and Natural Resources Practice has extensive experience advising clients on Prop 65 compliance and litigation. This subject matter focus is matched by the extensive First Amendment experience of WilmerHale's Appellate and Supreme Court Litigation Practice and Government and Regulatory Litigation Practice.

The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.