“Canada has a rather strict system compared to other jurisdictions […], Nonetheless, it is still quite navigable in practice with the guidance of an experienced practitioner.” – Herman Cheung
By Julius Melnitzer | March 16, 2026
Canada’s double patenting (DP) regime, which recognizes both “same invention” DP and “obviousness-type double patenting” (OTDP), but has no provision for United States (US)-style “terminal disclaimers”, leaves the country’s applicants as among the most vulnerable in the world to DP objections. Nonetheless, an experienced practitioner could help in clearing the minefield.
“Canada has a rather strict system compared to other jurisdictions,” says Herman Cheung, a senior associate in the Toronto office of Smart & Biggar, a member of the IPH network. “And there’s considerable uncertainty in it, because the statutory framework for double patenting is thin, and most of it is judge-made law. Nonetheless, it is still quite navigable in practice with the guidance of an experienced practitioner.”
Indeed, two recent developments—a Federal Court of Appeal (FCA) decision and the implementation of patent term adjustment (PTA)— may, in some cases, sharpen practical risk and uncertainty around DP.
Canadian DP has two branches. The first is the “same invention” branch. It catches cases where the later claims are identical or effectively coterminous in scope with the earlier claims. That is conceptually aligned with the US statutory “same invention” DP test, which is often described as a literal identity test. The second branch is the broader OTDP, a judicial doctrine preventing an unjustified extension of monopoly where the later claims are obvious in light of the earlier claims. That is the Canadian analogue to US OTDP, not to the US literal identity test.
The Canadian and American OTDP tests are conceptually similar. They both represent a second obviousness attack on patents by way of comparison from claim-to-claim rather than from claim-to-prior-art.
“There’s no question that the OTDP analysis makes things more complex during prosecution,” Cheung says. “This is because it adds a claim‑to‑claim, obviousness‑style comparison between related applications or patents, based on the claims and the common general knowledge, on top of the usual prior‑art analysis.”
But the Canadian OTDP analysis generally asks whether the claims of the later patent define an obvious or non-distinct invention over the claims of the earlier patent, even though both systems refer in various ways to “obvious variants” of earlier subject matter.
The US system, however, features a mechanism, called a “terminal disclaimer”, that allows applicants to overcome OTDP rejections in appropriate circumstances. Applicants who resort to terminal disclaimers agree that the later and earlier patents will expire at the same time. They also stipulate that the patents will be commonly owned until expiry, which prevents the patents from being separately owned and enforced. There is no analogous terminal disclaimer mechanism under Canadian law.
Further complicating the Canadian regime is the judge-made bifurcation of divisionals, recently a focus of DP disputes, into “forced” and “voluntary” categories. “Forced” divisionals are applications filed on the Commissioner’s direction in response to examiners’ unity objections; “voluntary” divisionals are applicant-initiated without examiner prompts.
Historically, many practitioners have taken comfort in the view that divisionals filed in response to a clear unity objection by the Patent Office were less susceptible to DP attacks, on the premise that they pursued subject matter the Commissioner had indicated was distinct; however, case law has emphasized that DP can still arise wherever a second patent claims an obvious, non‑distinct invention that confers an unjust additional benefit, including in the context of divisionals.
“The thinking has traditionally been that when examiners stated there was more than one invention, which ‘forced’ the divisional application, the resulting divisional patent should be safe from double-patenting because the parent and divisional do not share a single general inventive concept, and are considered distinct and separable inventions,” Cheung says.
But the FCA’s recent decision in NCS Multistage Inc. v. Kobold Corporation, which revisited DP principles, may change that perception. In a fact situation that involved voluntary divisionals, the FCA rejected the idea that a divisional is automatically protected from DP attacks simply because unity of invention has been raised in prosecution: while the court acknowledged that unity was relevant, the decision was also clear that it was not determinative.
In NCS Multistage Inc. v. Kobold Corporation, the Federal Court of Appeal confirmed that “voluntary” divisional patents can still be invalid for DP over their parent patents in Canada, even where they share the same expiry date. The court held that the focus of the DP analysis is whether the claims of the later patent represent an obvious, non‑distinct invention over the earlier patent, and that matching terms do not, by themselves, avoid a DP problem. The decision also underscored that, if a patentee wishes to rely on the idea that a divisional was “forced” in order to argue for different treatment, they must be able to trace the divisional back to a specific direction or requirement from the Commissioner. This traceability requirement raises further practical questions, including:
- How strictly will courts require patentees to demonstrate that a divisional was truly “forced” by the Commissioner, rather than simply being filed for strategic reasons?
- What types of communications or entries on the prosecution record will be sufficient to establish that traceability in litigation?
- To what extent, if any, will a finding that a divisional was properly “forced” actually limit the availability or scope of DP attacks?
Given the extent to which Canada’s DP doctrine is neither codified nor perfectly predictable, and given the structural tension between unity of invention requirements and the risk that patents issuing from divisional applications may be attacked, guidance from an experienced practitioner can help rights holders devise an effective divisional and DP avoidance strategy.
All the more so because Canada has introduced patent term adjustment (PTA), which in limited circumstances can add time to the term of a patent. PTA will not arise in every case, but it can result in related patents within a family having non-uniform expiry dates.
Where expiry dates diverge, DP considerations can take on added practical significance, because differences in expiry can sharpen focus on whether closely related subject matter is being pursued across multiple patents. In practical terms, this potential divergence may increase scrutiny of divisional strategies for DP risk, even though the doctrine remains a claim-to-claim inquiry.
It is a minefield, but an experienced practitioner is your minesweeper.
Julius Melnitzer is a Toronto-based writer who focuses on law, legal affairs, and the business of law. Follow him on LegalWriter.net or email him at julius@legalwriter.net.