When “It Works” Doesn’t Work:
Bayer v. Mylan and the Limits of Clinical Efficacy Claims

October 2, 2025

The Federal Circuit’s September 2025 decision in Bayer Pharma AG v. Mylan Pharmaceuticals Inc., No. 23-2434 (Fed. Cir. Sept. 23, 2025), is a significant recalibration of how U.S. patent law treats clinical trial results when grafted onto otherwise known therapeutic regimens. At issue was whether the phrase “amounts that are clinically proven effective” could rescue a dosing method from invalidation over prior art clinical trial disclosures. The Federal Circuit’s answer was a resounding no: when such language is functionally unrelated to the claimed invention, it cannot impart patentable weight.

This decision is not just a cautionary tale about claim drafting. It is a forceful reaffirmation of foundational doctrines—functional relationship, inherent anticipation, and the nexus requirement for secondary considerations—that together define the boundary between patentable invention and unprotectable discovery. It also carries significant strategic consequences for pharmaceutical and biotech innovators, who must now navigate an even narrower path between clinical validation and patent eligibility.

Bayer’s “Clinically Proven” Dosing Claims

Bayer’s U.S. Patent No. 10,828,310 (the “’310 patent”) claimed methods of reducing the risk of myocardial infarction, stroke, or cardiovascular death by administering rivaroxaban and aspirin in specified amounts. Claim 1 recited administering 2.5 mg rivaroxaban twice daily and 75–100 mg aspirin once daily, “wherein said amounts are clinically proven effective.”

The dispute arose because prior art references—including a published clinical trial protocol—had already disclosed the same dosing regimen, albeit without reporting final efficacy data. Bayer contended that the “clinically proven effective” language distinguished its invention by requiring demonstrated efficacy, something the prior art did not teach.

The Patent Trial and Appeal Board (PTAB) disagreed, finding the challenged claims anticipated and obvious. It concluded that the efficacy language was functionally unrelated to the claimed method and could not overcome the prior art. Bayer appealed. The Federal Circuit affirmed in part and vacated in part, but most importantly, it endorsed the Board’s central holding: functional unrelatedness renders result-oriented claim language non-limiting for patentability purposes. Bayer, slip op. at 13–17.

Functional Relationship: A Reasserted Limiting Principle

The doctrine that claim limitations must have a “functional relationship” to the claimed invention traces its roots to early 20th-century jurisprudence. The Supreme Court’s decision in Parker v. Flook, 437 U.S. 584 (1978), articulated the principle that “post-solution activity” or a mere “field of use” cannot transform an otherwise unpatentable concept into patentable subject matter. Id. at 590. While Flook addressed § 101, its underlying reasoning—that a limitation must meaningfully change the claimed invention to carry patentable weight—has been applied across patent doctrines.

The Federal Circuit has repeatedly reaffirmed this requirement. In In re Ngai, 367 F.3d 1336 (Fed. Cir. 2004), the court rejected an attempt to distinguish prior art by adding a “kit” limitation to a known method of testing blood glucose, holding that the new language lacked a functional relationship to the claimed steps. Id. at 1338–39. Likewise, in In re Kao, 639 F.3d 1057 (Fed. Cir. 2011), the court held that a “food effect” limitation describing how a formulation behaved when ingested with food did not distinguish the claim from prior art formulations when the physical composition was unchanged. Id. at 1070.

The Bayer court applied this same principle. It found that the phrase “amounts that are clinically proven effective” did not alter how the method was practiced. The dosing regimen remained the same regardless of whether efficacy had been demonstrated. The phrase described a result rather than imposed an operative constraint. Bayer, slip op. at 14–15. As the court explained, “the limitation does not change the physical steps of the method, nor does it require any additional acts by the practitioner.” Id. at 15.

This reasoning resonates with General Electric Co. v. Jewel Incandescent Lamp Co., 326 U.S. 242 (1945), which rejected claims that merely described the “characteristics” of a known lamp filament, and In re Swinehart, 439 F.2d 210 (C.C.P.A. 1971), which cautioned that “the discovery of a property” of a known composition does not make the composition patentable absent a new structural feature. Id. at 212. Bayer’s attempt to patent the clinical property of a known regimen runs afoul of this same principle.

Inherent Anticipation and the Irrelevance of Post Hoc Results

The Federal Circuit’s decision also rests on the doctrine of inherent anticipation, which holds that an express disclosure is unnecessary if the prior art necessarily performs the claimed function or achieves the claimed result. Atlas Powder Co. v. IRECO Inc., 190 F.3d 1342, 1347 (Fed. Cir. 1999) (“[I]nherent anticipation does not require that a person of ordinary skill recognize the inherent characteristic or function.”). The classic example is In re Cruciferous Sprout Litigation, 301 F.3d 1343 (Fed. Cir. 2002), where prior art teaching the consumption of cruciferous sprouts inherently disclosed their cancer-preventive properties, even though those properties were unknown at the time. Id. at 1349.

So too here. The prior art disclosed the same dosing regimen. Whether or not clinical efficacy had been demonstrated at the time, the regimen either was or was not clinically effective. If it was, that property was inherent; if it was not, Bayer’s claim failed on enablement grounds. Either way, the efficacy language could not confer novelty.

The court’s reasoning echoes its decision in Schering Corp. v. Geneva Pharmaceuticals, Inc., 339 F.3d 1373 (Fed. Cir. 2003), where a metabolite was held inherently anticipated by prior art disclosing its parent compound. Id. at 1377. Just as a patentee cannot claim a metabolite formed inevitably from a known drug, Bayer cannot claim the inevitable clinical property of a known dosing regimen. As Atlas Powder makes clear, “[t]he discovery of a previously unappreciated property of a prior art composition, or of a scientific explanation for the property, does not render the old composition patentably new.” 190 F.3d at 1347.

Secondary Considerations and the Nexus Requirement

Bayer’s fallback argument rested on secondary considerations—specifically, that the regimen’s clinical efficacy was unexpected and therefore evidence of nonobviousness. But as the Federal Circuit reiterated, secondary indicia require a nexus to the claimed invention. Fox Factory, Inc. v. SRAM, LLC, 944 F.3d 1366, 1373 (Fed. Cir. 2019). A patentee must show that the proffered evidence “is the direct result of the unique characteristics of the claimed invention.” Id. at 1375.

Here, because the “clinically proven effective” limitation was functionally unrelated, there was no nexus between the unexpected results and the claimed method. Bayer, slip op. at 17. This holding builds on Kao, where evidence of unexpected pharmacokinetic behavior could not establish nonobviousness because it was not tied to a claim limitation that distinguished the invention from the prior art.

The decision also underscores the danger of relying on post hoc clinical data to establish nonobviousness. As the Supreme Court observed in Graham v. John Deere Co., 383 U.S. 1, 17–18 (1966), secondary considerations are relevant but “must always be considered in connection with the facts establishing obviousness.” When the claim language itself contributes nothing new, secondary considerations become irrelevant.

Clinical Trial Protocols as Prior Art and the Public Disclosure Trap

A further layer of complexity in Bayer is the role of clinical trial protocols as prior art. The references at issue included published protocols that disclosed the same doses and administration schedules, though not final results. The court treated those disclosures as anticipating prior art. Bayer, slip op. at 12–13.

This approach is consistent with In re Montgomery, 677 F.3d 1375 (Fed. Cir. 2012), where the court held that a clinical protocol disclosing the same dosing regimen anticipated a later claim even though the protocol’s results were unknown. The Federal Circuit reasoned that a reference “need not demonstrate efficacy to anticipate” a therapeutic method claim; disclosure of the method itself is sufficient. Id. at 1380–81.

The tension for drug developers is obvious: regulatory obligations such as ClinicalTrials.gov registration require disclosure of trial designs, including dosage and patient population. These disclosures, even without efficacy data, may later serve as prior art. Bayer underscores that once such disclosures are public, adding a “clinically proven” gloss will not revive the patentability of the underlying regimen.

Strategic Implications for Life Sciences Patent Practice

The Bayer decision carries significant strategic implications for pharmaceutical and biotechnology companies, particularly those seeking to protect dosing regimens, repurposed drugs, and combination therapies.

First, early filing is paramount. As Montgomery and now Bayer illustrate, once trial protocols are public, they can anticipate later-filed claims. Companies should consider filing applications before public disclosure of protocol details to preserve patent rights.

Second, tie efficacy to structure or method. As Bayer demonstrates, result-oriented language is vulnerable if it does not change how the method is practiced. Draft claims that incorporate efficacy-related features as operative limitations—such as specific biomarkers, pharmacokinetic parameters, or titration schedules—rather than as descriptive outcomes.

Third, manage the nexus problem proactively. If secondary considerations are part of your nonobviousness strategy, ensure that your claims include limitations directly linked to those results. Evidence of unexpected efficacy is meaningless if the claim language that allegedly produced it is disregarded as functionally unrelated.

Fourth, monitor public disclosures. Protocol registration, conference abstracts, and investor communications can all create prior art. Patent and regulatory teams must coordinate closely to ensure that disclosures do not preempt patent rights.

Broader Doctrinal Significance: Reinforcing the Discovery–Invention Divide

Perhaps the most significant contribution of Bayer is its reaffirmation of a foundational patent law principle: discoveries of natural properties, inherent results, or post hoc observations are not patentable inventions. This principle is evident across multiple doctrines—§ 101 (Flook), anticipation (Atlas Powder), obviousness (Graham), and functional limitation (Ngai, Kao). The Federal Circuit’s decision integrates these strands into a coherent doctrinal statement: a patent claim must define an invention in structural or procedural terms, not merely describe what the prior art does or achieves.

This distinction has special salience in life sciences. As the Federal Circuit observed in Cruciferous Sprout, the fact that scientists later recognized a new property of an old method does not render the method patentable. Likewise, in Abbott Labs. v. Baxter Pharm. Prods., Inc., 334 F.3d 1274, 1277 (Fed. Cir. 2003), the court held that a newly discovered property of a known anesthetic composition did not confer novelty. Bayer follows this same logic: clinical proof of efficacy, even if newly discovered, cannot make an old dosing regimen new again.

Beyond Bayer

Bayer is a decisive reaffirmation of long-standing principles in patent law, but it also reshapes the strategic landscape for life sciences innovators. It tells us that functional unrelatedness remains a formidable barrier, that inherent properties cannot rescue otherwise anticipated claims, and that secondary considerations require a real nexus to patentable subject matter. It warns that clinical trial protocols themselves may serve as prior art, even before results are known.

More broadly, the decision signals a judicial insistence on the distinction between discovery and invention. Discovering that a known method “works” in a particular way is not enough. To merit patent protection, a claim must define how the method is done differently—not merely what happens when it is done.

For patent prosecutors and litigators alike, Bayer is both a roadmap and a caution sign. It demands greater precision in claim drafting, tighter coordination with clinical disclosure strategies, and a more disciplined approach to integrating clinical evidence into patent arguments. And it stands as a reminder that in the eyes of the Federal Circuit, the boundary between science and patent law is not drawn at the publication of a trial result—it is drawn at the moment an idea becomes an invention.