Obviousness-Type Double Patenting

What is obviousness-type double patenting?

Obviousness-type double patenting (ODP) is a judicially created doctrine — not codified in the Patent Act — that prevents a patent applicant from extending patent term by obtaining multiple patents on obvious variations of the same invention. The doctrine prevents 'unjustified timewise extension of patent rights' beyond a single patent term. The test: are the claims of the later application an obvious variation of the claims (not the specification) of the earlier patent? If yes, the later application claims cannot be patented unless a terminal disclaimer is filed. ODP differs from statutory double patenting (which is explicitly prohibited and non-cureable) because ODP involves obvious variants, not identical claims.

Terminal disclaimers: the standard cure

A terminal disclaimer (TD) is the standard mechanism for overcoming an ODP rejection. The patent owner files a TD in the later application/patent agreeing that: (1) the later patent will expire on the same date as the reference patent (tying the expiration dates); and (2) the later patent will only be enforceable while it is commonly owned with the reference patent. The TD is filed using Form PTO/SB/25 with a modest fee. TDs are used extensively in pharmaceutical and technology patent families — any continuation application that claims obvious variants of the parent's claims will typically require a TD. The downside of a TD: if two linked patents are ever separated in ownership (e.g., one is sold, licensed exclusively, or spun off), they lose enforceability.

How ODP rejections are examined

When an examiner issues an ODP rejection, they compare the claims of the pending application to the claims (not the specification) of a reference patent or published application owned by the same inventive entity. The comparison uses the same two-step approach as § 103 obviousness: are the claim differences obvious in light of the reference claims? The analysis is often shorthand: an ODP rejection may simply cite that the pending claims are obvious variants of parent claims. Unlike a § 103 rejection requiring specific prior art, an ODP rejection only requires showing that the claims are directed to patentably indistinct subject matter. The solution — a terminal disclaimer — doesn't require arguing that the claims are non-obvious; it simply accepts the relationship and ties the terms.

Common ownership requirement: the hidden risk

The most dangerous aspect of terminal disclaimers is the common-ownership requirement. When a terminal disclaimer is filed, all patents linked by the TD must be commonly owned throughout their term to be enforceable. If Pharma Co. files continuation patents A, B, and C — all linked by TDs to the original patent — and then licenses only patent B exclusively to a licensee (who now has title for enforceability purposes), patent B may lose its TD-linked enforceability because it is no longer commonly owned with patents A and C. This risk is present in: (1) exclusive patent licenses with assignment-level rights; (2) spin-off transactions where some but not all patents in a family are transferred; (3) M&A where the acquiree has a large TD-linked family. Patent portfolio buyers and licensees need to carefully audit TD relationships before transactions.

ODP in pharmaceutical patent families

ODP is particularly significant in pharmaceutical patents because drug companies frequently file continuation applications to pursue claims directed to specific formulations, dosing regimens, methods of use, metabolites, and combinations related to an active ingredient. Each continuation application faces potential ODP rejection based on the parent's granted claims. The TD requirement effectively ties all these patents' expiration dates to the earliest-expiring patent in the family. This limits one strategy for extending exclusivity — filing continuation after continuation to extend the effective patent coverage period — because all TDs in the chain expire with the earliest patent. Hatch-Waxman patent listings in the Orange Book are affected by TD-linked expiration dates: the listed expiration date must account for the TD.

AIA safe harbor under § 121

35 U.S.C. § 121 provides a limited safe harbor from ODP for patents arising from restriction requirements. When a USPTO examiner issues a restriction requirement — finding that a single application claims two or more independent and distinct inventions — and the applicant elects one invention, the divisional applications filed for the other inventions are protected from ODP rejections based on the restriction requirement. The safe harbor only applies to the specific inventions identified in the restriction requirement; it does not protect claims that overlap with the elected application's claims. The safe harbor is frequently litigated in pharmaceutical ODP cases because pharma applicants may argue that continuation claims should benefit from a restriction requirement issued in the parent. Courts strictly construe the § 121 safe harbor.

USPTO 2024 proposed rule and its implications

In May 2024, the USPTO proposed a controversial rule change that would significantly alter how terminal disclaimers work. Under the proposal, a TD filed to overcome ODP would make the disclaimed patent unenforceable — not just expire together — if the reference patent is determined to be invalid by any forum (court or PTAB). This would create a vulnerability: a defendant could challenge one patent in a TD-linked family and, if successful, automatically invalidate all patents linked to it. The proposal drew massive pushback from pharmaceutical and biotechnology companies with large continuation patent families. As of mid-2025, the rule's final status was unresolved. Practitioners building continuation strategies should stay current on this development.

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