The US Supreme Court’s recent decision on glyphosate-based herbicide litigation has exposed a critical conceptual gap: while courts and scientists both use the word “causation,” they are answering fundamentally different questions about risk and responsibility. This distinction, rarely articulated in public discourse, carries profound implications for how medical evidence shapes legal outcomes and public health policy.
Key takeaways
- The Supreme Court’s Roundup ruling illustrates how legal causation (did this product cause this person’s harm?) differs from scientific causation (is there a causal mechanism and population-level evidence of association?)
- Epidemiologists assess causation through multiple criteria—biological plausibility, dose-response relationships, and consistency across studies—while courts focus on individual liability and proximate cause
- This divergence creates legal outcomes that may not align with scientific consensus, raising questions about how medical evidence should inform regulatory and civil law decisions
How Science and Law Define Causation Differently
Core differences in how each discipline establishes causal relationships
Source: Epidemiological principles vs. legal doctrine | Georgian Medical Journal News
The Supreme Court’s decision and what it revealed
In a recent ruling on glyphosate litigation—a case central to thousands of product liability suits—the Supreme Court applied legal causation standards that hinged on whether a specific plaintiff could show that the herbicide caused their cancer. However, the epidemiological literature on glyphosate presents a more nuanced picture: meta-analyses and systematic reviews in toxicology and occupational health journals have examined population-level associations between exposure and lymphomas, but individual-level causation remains contested.
This raises a critical question that rarely surfaces in legal proceedings: is the absence of conclusive population-level scientific evidence sufficient to dismiss individual claims, or does legal causation operate under a different standard altogether? The Court’s reasoning suggests the former, yet epidemiologists emphasize that absence of evidence is not evidence of absence—particularly when exposure is difficult to quantify retrospectively at the individual level.
How epidemiologists and lawyers use “causation” differently
Epidemiologists employ the Bradford Hill criteria for assessing causation, a framework developed in 1965 that examines strength of association, biological gradient (dose-response), consistency across studies, temporal sequence, biological plausibility, and coherence with existing knowledge. These criteria allow for probabilistic reasoning: an exposure may increase cancer risk by 30% in a population, even though individual cases remain multifactorial.
In contrast, courts apply legal causation standards rooted in tort law: “but for” causation (would the injury have occurred without the defendant’s action?) and proximate cause (was the harm a foreseeable result?). Critically, legal causation often requires showing causation “more likely than not” for a specific individual—a threshold that is conceptually distinct from epidemiological probability. A plaintiff must demonstrate that the defendant’s product, more likely than not, caused their particular cancer, not merely that it elevated risk in a population.
This divergence explains why expert testimony by epidemiologists in product liability cases frequently becomes a point of contention. Epidemiologists testifying about population-level risk may find their testimony deemed insufficient under legal standards requiring individual-level causation.
Regulatory agencies and the grey zone
The regulatory landscape adds another layer of complexity. The US Environmental Protection Agency (EPA) concluded that glyphosate is “not likely to be carcinogenic to humans”, while the International Agency for Research on Cancer (IARC), a WHO subsidiary, classified it as “probably carcinogenic” (Group 2A) in 2015. Both agencies reviewed similar evidence but reached different conclusions—a divergence that highlights how causation itself can be interpreted differently by experts operating under different regulatory mandates.
The EPA’s assessment emphasized controlled human studies and mechanistic data, while IARC weighted epidemiological evidence of association more heavily. Neither framework is inherently wrong; they reflect different precautionary thresholds. However, when a court must decide whether a product caused individual harm, the existence of regulatory disagreement becomes legally weaponized: plaintiffs cite IARC; defendants cite EPA. The jury is left to parse expert disagreement that reflects methodological and philosophical differences, not necessarily scientific uncertainty alone.
The Supreme Court’s decision illustrates a fundamental truth: causation is not a single concept but a framework chosen based on the question being asked and the stakes involved.
— Epidemiological and legal analysis, GMJ News (2026)
Implications for evidence-based practice and policy
For clinicians and occupational health professionals, this divide has practical consequences. When a patient presents with non-Hodgkin’s lymphoma and reports long-term pesticide exposure, the physician must navigate a confusing landscape: what does the scientific evidence show, what has the law said, and what is the clinical relevance? The occupational history remains a critical component of cancer diagnosis and management, yet the medico-legal framing of causation can obscure rather than clarify clinical assessment.
For policymakers, the misalignment between legal and scientific causation creates governance challenges. Regulatory decisions ideally rest on causal inference; legal decisions must assign liability. When the two systems produce conflicting conclusions, public trust in institutions erodes. A more transparent acknowledgment of these different frameworks—and explicit communication about which standard applies in which context—could improve both scientific communication and public understanding of risk.
What this means
Frequently asked questions
Why did the Supreme Court and IARC reach different conclusions about glyphosate?
The EPA and IARC applied different evidentiary standards and regulatory philosophies. IARC weighted epidemiological evidence of association and mechanistic data suggesting carcinogenic potential; the EPA emphasized controlled human studies and applied a higher causality threshold. Both interpretations are scientifically defensible but reflect different approaches to precaution and evidence.
Can an individual be harmed by a product that a regulator has approved as safe?
Yes. Regulatory approval at the population level does not preclude individual susceptibility. Some people may develop hypersensitivity or experience adverse effects at doses tolerated by most. Regulatory causation (population-level safety) and individual causation (did this exposure harm this person?) are distinct questions.
How should I interpret conflicting expert testimony in product liability cases?
Conflicting expert opinions often reflect differences in how causation is framed—epidemiological versus legal—rather than disagreement about scientific facts. Ask whether experts are discussing population-level association, individual liability, or regulatory risk. Understanding these distinctions clarifies the nature of expert disagreement.
The Supreme Court’s Roundup ruling has inadvertently performed a public service: it has highlighted a conceptual confusion that pervades the intersection of science and law. Until courts, regulators, and scientists develop more transparent language about which causation framework applies in which context, litigation will continue to conflate distinct questions, and public understanding of evidence will remain fragmented. Clear terminology—distinguishing regulatory, scientific, and legal causation—is essential for better policy and informed public debate about chemical safety and individual responsibility.
Source: Opinion: Supreme Court ruling on Roundup points to a confusing difference between the law and science, STAT News
Was this article helpful?
Disclaimer. This article is health journalism intended for general information and education. It is not medical advice and is not a substitute for professional diagnosis or treatment. Always consult a qualified healthcare provider about your individual circumstances. Full disclaimer →
Related Coverage
Editorial standards. This article was produced under the GMJ News editorial process, with oversight by the GMJ Editorial Board. Our editorial process. Spotted an error? Contact the editorial team.
