Key Takeaway: After In re Cellect and Allergan v. MSN clarified the application of obviousness-type double patenting in the context of patent term adjustment, a new question has emerged: Can an obviousness-type double patenting rejection rest solely on the risk of harassment, even when no patent term is extended? The USPTO’s Appeals Review Panel has answered yes. The Federal Circuit is now poised to address that question in In re Ablynx.

Introduction
Obviousness-type double patenting (ODP) is a judicially created doctrine to prevent patentees from improperly extending exclusivity by obtaining successive patents on obvious variants of an invention. The doctrine rests on two rationales: preventing an unjustified extension of patent exclusivity and protecting accused infringers from harassment by different assignees of patents claiming patentably indistinct inventions. A terminal disclaimer generally addresses both concerns by disclaiming any term extending beyond the reference patent’s expiration and conditioning enforceability on common ownership. Applicants, however, are understandably reluctant to accept these restrictions. Challenges to the circumstances in which those restrictions are required continue to shape the doctrine’s development.

Term Extension
A patent’s term generally runs twenty years from its earliest effective U.S. nonprovisional filing date, so related patents sharing that date ordinarily expire together.  Patent term adjustment (PTA) for USPTO delay, however, can cause those expiration dates to diverge, potentially raising ODP issues.

In In re Cellect, LLC, the court held that ODP must be assessed using a patent’s expiration date after accounting for PTA. 81 F.4th 1216, 1226-29 (Fed. Cir. 2023). Thus, a patent that expires later than a related patent solely because of PTA can be invalidated over the earlier expiring related patent in the absence of a terminal disclaimer. Id. In Cellect, each challenged patent traced back to a family member that had received no PTA.  No terminal disclaimers had been filed, and the challenged patents had already expired, foreclosing that remedy. The court rejected the argument that invalidity should be limited to the PTA period, reasoning that this would effectively permit a retroactive terminal disclaimer after expiration. Id. at 1230–31.

The following year, the Federal Circuit clarified the limits of that holding in Allergan USA, Inc. v. MSN Laboratories Private Ltd., 111 F.4th 1358 (Fed. Cir. 2024). In Allergan, the challenged parent patent was the first-filed and first-issued patent in its family but, because of PTA, expired after two later-filed continuations asserted as ODP references. Id. at 1362–63. The court held that a first-filed, first-issued, later-expiring claim cannot be invalidated for ODP by a later-filed, later-issued, earlier-expiring reference claim sharing a common priority date. Id. at 1369; see also Acadia Pharmaceuticals Inc. v. Aurobindo Pharma Ltd., No. 2024-1401, 2025 WL 1618201 (Fed. Cir. May 15, 2025) (applying Allergan to affirm judgment of no invalidity,). The first-filed, first-issued patent, the court explained, “sets the maximum period of exclusivity” for the invention and its obvious variants. Allergan, 111 F.4th at 1369–71. In reaching that conclusion, Allergan distinguished Cellect as addressing how PTA affects the expiration date used in an ODP analysis, rather than which patent may serve as an ODP reference. Id. at 1368–69.

The USPTO’s interpretation of Allergan has revealed differing approaches within the Board. In Ex Parte Baurin, the Appeals Review Panel construed Allergan’s “first-filed” requirement to mean the first filing in the patent family. No. 2024-002920, 2026 WL 2322413, at *7 (PTAB Aug. 6, 2026) (“Baurin III”). Under that narrow construction, the panel instructed examiners to continue pre-Allergan ODP practice unless (1) the application (or patent under reexamination) and the ODP reference belong to the same family and share the same effective filing date (the date used to calculate patent term), and (2) the claims under examination are first-filed, first-issued, and later-expiring. Id. at *17. The panel acknowledged that these circumstances rarely arise outside reexamination or reissue. Id. Yet approximately two months earlier, a different Board panel had applied Allergan more broadly in Ex parte Corteva Agriscience, LLC, reversing an ODP rejection where the challenged patent was filed and issued before the asserted reference but expired later due to 1,165 days of PTA, even though it was not the first patent in the family. 2026 WL 1696375, at *5-6 (PTAB June 9, 2026). The panel reasoned that Allergan’s holding turns on the relative relationship between the challenged and reference patents, rather than their absolute position within the family. Id. at *3–4. The decisions thus reflect competing readings of Allergan: whether its protection depends on a patent’s position within the entire family or only its relationship to the asserted ODP reference.

The Anti-Harassment Rationale
Recent Board decisions have also examined ODP’s second rationale—preventing multiple assignees of patentably indistinct patents from harassing an accused infringer.

In Ex parte Baurin, a Board panel reversed an ODP rejection because any patent issuing from the challenged application would expire before the reference patent, and that a terminal disclaimer over that reference would therefore have no effect on the challenged application’s patent term.  No. 2024-002920, 2024 WL 4921198, at *5-6 (PTAB Nov. 6, 2024) (“Baurin I”). The Board concluded that the reference was improper and that the risk of separate ownership was immaterial in the absence of a proper ODP reference.  See id. at *5, n. 6. In a Request for Rehearing, the Examiner argued that precedent, including In re Cellect, establishes that the risk of separate ownership is sufficient to support an ODP rejection.  However, the Board disagreed explaining that “no court has held that risk of common ownership is a sole justification for upholding an ODP rejection that is not based on a proper reference patent.” No. 2024-002920, 2025 WL 3720240, at *13 (PTAB Dec. 12, 2025) (“Baurin II”).

On sua sponte review, the Appeals Review Panel reversed, holding that harassment risk is an independent basis for ODP under binding precedent.  Baurin III, at *11. However, the panel expressed discomfort with that rule and invited clarification from the Federal Circuit. See id. The panel outlined a possible future framework that included: screening references by patent-term filing date, barring later-filed progeny from invalidating earlier-filed parents, and either abandoning the anti-harassment rationale as a standalone basis for ODP or requiring evidence of actual divided ownership or reciprocal obviousness before harassment could sustain a rejection. See id. at *12-17.

Whether the risk of harassment alone can support ODP is now before the Federal Circuit in In re Ablynx N.V., No. 2026-1333 (Fed. Cir.), an appeal from Ex parte Baumeister, No. 2026-000193, 2025 WL 3515282, at *10-11 (PTAB Nov. 20, 2025). On facts the Appeals Review Panel described as nearly identical to those in Baurin, a different Board panel affirmed ODP rejections under the anti-harassment rationale where the references came from different families with later filing and expiration dates. See id. Briefing is complete and the USPTO relies heavily on In re Fallaux, 564 F.3d 1313 (Fed. Cir. 2009) as controlling precedent. Ablynx argues, however, that Fallaux resolved only whether a one-way or two-way obviousness standard governs—not that anti-harassment is an independent ODP ground.

Take-home guidance
Practitioners should exercise caution when relying on Allergan beyond the specific circumstances identified in that decision and recognized by the Appeals Review Panel. Pending a decision in Ablynx, owners of commonly owned patents containing patentably indistinct claims should consider whether protective terminal disclaimers or, where procedurally available, amendments that render the claims patentably distinct are warranted before the earliest expiration date in the relevant family and before asserting the patents.  Where timing permits, however, practitioners may wish to defer filing terminal disclaimers until Ablynx clarifies the doctrine—particularly where no term extension is at stake and common ownership is secure.

Conclusion
Obviousness-type double patenting continues to evolve rapidly. The recent USPTO decisions and the pending Federal Circuit appeal have laid a road map for its next development. With a decision expected next year, In re Ablynx is the case to watch.

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