The Supreme Court ruling in Monsanto v. Durnell does not address whether glyphosate in Roundup causes cancer, clarifying that federal pesticide law preempts state failure-to-warn claims when no cancer warning is mandated by the EPA. The article contrasts scientific and legal definitions of causation, noting that while science assesses causation through population studies, law requires a direct link to the plaintiff's specific injury. This confusion is evident in various litigations, including glyphosate and talc cases, where jury decisions do not equate to scientific consensus. The author emphasizes the need for clarity in understanding these distinctions to maintain public trust in both scientific findings and legal rulings.

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Supreme Court ruling on Roundup points to a confusing difference between the law and science

Science and law use the word ‘causation’ to mean very different things

Justin Sullivan/Getty Images

By Alex Smolak

June 27, 2026

Smolak is an epidemiologist with the Infectious Disease Epidemiology Group at Weill Cornell Medicine-Qatar.

When the Supreme Court handed Monsanto a major win in Roundup litigation on Thursday, the headlines sounded like a scientific event: a case about whether Roundup causes cancer.

But Monsanto v. Durnell did not settle that question. The court held that federal pesticide law preempts a state failure-to-warn claim when the Environmental Protection Agency has not required a cancer warning on the product label.

That is an important legal ruling. It is not the same thing as a scientific finding that glyphosate is safe or unsafe.

The ruling is just the most recent example of a serious problem: Science and law use the same word — causation — while asking different questions.

My own work has moved between clinical care, population-health research, and law, and that border is where this confusion becomes most visible. In epidemiology, causation is usually a population-level inference. Researchers ask whether an exposure reliably changes disease risk across groups of people. That requires replication, statistical association, dose-response evidence, biological plausibility, and efforts to rule out confounding. Even then, conclusions remain probabilistic. A risk factor can increase disease likelihood without proving why one person became ill.

The legal system has a different task. In civil litigation, the plaintiff generally must show that the specific injury would probably not have occurred without the defendant’s conduct. That standard does not exist to produce scientific consensus. It exists to resolve disputes.

That distinction explains why glyphosate litigation has been so confusing. In 2015, the International Agency for Research on Cancer classified glyphosate as probably carcinogenic to humans. The U.S. Environmental Protection Agency and the European Food Safety Authority have not reached the same conclusion under their regulatory frameworks. A jury, however, does not decide the global scientific status of glyphosate. It hears a particular plaintiff’s case: exposure history, diagnosis, expert testimony, internal documents, warnings, corporate conduct, and credibility. A plaintiff verdict may mean the legal threshold was met. It does not mean the broader scientific community has reached one settled conclusion.

Talc litigation shows the same problem in another form. Johnson & Johnson and other defendants have faced claims that talc-based products contributed to ovarian cancer or mesothelioma. Some claims focus on talc itself. Others focus on alleged asbestos contamination, a different issue because asbestos is a well-established carcinogen. In 2024, IARC classified talc as probably carcinogenic to humans, based on limited evidence in humans, sufficient evidence in experimental animals, and strong mechanistic evidence.

That classification matters. But it still does not mean every cancer occurring after talc use was caused by talc.

The scientific question is specific: Does talc, asbestos-contaminated talc, or perineal talc use reliably increase cancer risk across populations, under what exposure conditions, and with what level of confidence? The courtroom question is different: Would this plaintiff’s injury have occurred but for the product exposure, and was that causal link legally sufficient to assign responsibility?

Talc litigation also shows why juries do not evaluate causation in a sterile scientific vacuum. Plaintiffs may argue not only epidemiology, but corporate knowledge, internal documents, inadequate warnings, disputed testing practices, and alleged concealment. If jurors believe a company acted deceptively, they may interpret ambiguous scientific evidence more aggressively.

The problem is intensified because people are uncomfortable with randomness. Cancer feels too consequential to attribute to background risk, chance, or multifactorial vulnerability, so jurors and the public naturally search for a concrete cause.

These same dynamics are now playing out in litigation over social media and youth mental health.

States, school districts, and families are asking courts to determine whether platforms such as Instagram, TikTok, Snapchat, and YouTube contributed to anxiety, depression, self-harm, addictive use, educational disruption, and public costs. Some cases have already settled. To the public, these cases can sound like a scientific finding: Social media caused teen depression.

But the scientific question is harder.

Researchers must ask whether social media exposure or specific platform design features independently causes mental health outcomes across populations. That requires separating social media use from adolescent distress, loneliness, family instability, sleep disruption, bullying, genetics, psychiatric vulnerability, pandemic effects, and reverse causation. Depressed or socially isolated adolescents may use social media differently from those who are not. Heavy use may be a cause, a consequence, or both.

A cautious scientific conclusion does not mean social media is harmless. It does not mean specific platform features cannot contribute to injury. It means the causal question is multifactorial and difficult to isolate.

Courts still may move forward because they are not designed to wait for perfect causal certainty. The legal question may be whether platform design choices, including algorithmic recommendations, infinite scroll, notifications, engagement loops, filters, or addictive design features, foreseeably contributed to harm in particular users or imposed costs on schools and public systems. Internal documents, warnings, product design, foreseeability, and corporate conduct may matter legally even when population-level science remains unsettled.

Asbestos provides a useful contrast.

In asbestos litigation, legal causation and scientific consensus are often closely aligned. The causal relationship between asbestos exposure and mesothelioma is strong, well-established, and widely accepted. Courts are not operating in the same zone of scientific uncertainty that surrounds many glyphosate, talc, or social media claims.

I’m not saying that plaintiffs are always wrong or that courts should ignore harm until science reaches absolute certainty. The argument is narrower: Not every legal finding, verdict, or settlement carries the same scientific meaning.

Sometimes law and science converge. Sometimes courts assign responsibility in individual disputes while the broader scientific evidence remains mixed, unsettled, or difficult to translate into individual causation.

Public confusion arises when those situations are collapsed into one category.

Large jury awards can make scientific causation appear settled when it is not. Settlements can make legal exposure appear equivalent to admitted causation when it is not. Regulatory disagreement can make the public assume corruption when the real issue may be different evidentiary standards. Scientific caution can look like evasion. Legal accountability can look like scientific proof. Neither interpretation is reliable.

Science is designed to estimate risk, test hypotheses, identify patterns, and reduce the likelihood of false causal inference. Law is designed to resolve disputes, assign responsibility, compensate injury, deter misconduct, and impose duties. Those functions are related, but not the same.

This distinction matters for public trust. If people believe a jury verdict proves scientific consensus, later scientific caution may look corrupt. If people believe regulatory caution invalidates every legal claim, courts may look irrational. If people believe a settlement proves causation, the absence of admitted liability may look like evasion.

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So what should be done?

First, courts and lawyers should be more explicit about which causal question is being answered: general causation, specific causation, regulatory risk, failure to warn, product design, foreseeability, or legal preemption.

Second, expert testimony and public reporting should keep those categories separate. A hazard classification is not the same thing as proof that a product caused one plaintiff’s injury. A settlement is not the same thing as admitted causation. A regulatory decision is not the same thing as a jury verdict. A Supreme Court preemption ruling is not the same thing as a scientific exoneration.

Journalists have a role here, too. Coverage of cases involving Roundup, social media, talc, and other tricky topics should tell readers not only who won, but what question the court actually answered. Monsanto v. Durnell was a landmark ruling about federal pesticide labeling and state tort law. It was not a final scientific verdict on glyphosate.

Public trust will keep eroding if every legal outcome is treated as though it were a scientific finding. A courtroom can assign responsibility without settling science. Science can remain cautious without denying harm. And courts can limit liability without proving that a product is harmless.

Alex Smolak, Ph.D., is an epidemiologist with the Infectious Disease Epidemiology Group at Weill Cornell Medicine-Qatar.

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Supreme Court ruling on Roundup points to a confusing difference between the law and science

Supreme Court ruling on Roundup points to a confusing difference between the law and science

Science and law use the word ‘causation’ to mean very different things

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