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Understanding the Invalidation of Patents Post-Grant in Canada and the United States

By: Christopher Heer, Michelle Huong | Last updated: May 30, 2023


In Canada and the United States, issued patents are presumed to be valid for a period until 20 years from its filing date assuming all post-issuance maintenance fees are paid.

There are a number of situations where one might attempt to invalidate a patent. For instance, invalidating a patent is a defensive strategy against an infringement claim. For example, a patentee may bring suit and allege that a defendant has infringed on the patent in question. As a defence, the defendant may assert the patent is invalid, and therefore there can be no infringement.

Patents in Canada may be invalidated via re-examination and impeachment proceedings. In the United States, patents may be invalidated through inter partes review, ex parte re-examination proceedings, and litigation commenced in the Federal District Court.

The following sections will set out some of the key procedural and substantive considerations for the above-mentioned procedures.

Invalidating patents in Canada


Any person, including the patentee, may request that one or more claims of a patent granted after October 1, 1989, be re-examined by the Patent Appeal Board. Requests for re-examination may be made at any time during the term of an issued patent.

Re-examination is an opportunity for re-considering patent claims or an alternative to an impeachment proceeding. Compared to an impeachment proceeding, re-examinations do not involve live witnesses under cross-examination or testing of issues of fact.

Requirements for requesting re-examination

A valid request for re-examination requires filing a written request and payment of the requisite fee. In addition, the request must include prior art, which will be considered during the re-examination process. Examples of the prior art include patents, patent applications open for public inspection and printed publications. Further, the requesting party must explain why the included prior art anticipates or renders obvious the claim or claims the requesting party seeks to invalidate. If the requesting party only discusses the pertinence of the prior art in relation to some but not all claims requested for re-examination, then only the claims supported by the explanation will be considered for re-examination.

Re-examination proceedings

Once the Commissioner of Patents reviews the request, if the requesting party is not the patentee, then a package consisting of a copy of the request and prior art will be sent to the patentee. No package is sent if the requesting party is also the patentee.

After which, the Commissioner of Patents will establish a re-examination board, which will consist of no less than three persons, at least two of whom are employees of the Patent Office. The re-examination board members must not have participated nor have advised in the examination process of the patent that is to be re-examined. Unlike a competitor in an impeachment proceeding, the re-examination board is not an adverse party to the patentee. Rather, the re-examination board functions as an adjudicator and the re-examination process is part of its statutory duties.

First stage

After a requesting party submits an examination request and accords with the rules, re-examination will proceed in two stages. At the first stage, the re-examination board will determine if the re-examination request raises a substantial new question of patentability.

A substantial new question of patentability must not be related to nor closely related to validity issues of one or more claims considered during the prosecution process that led to the grant of the patent or any prior proceeding involving the granted patent.

Typically, a substantial new question of patentability is raised in the context of prior art that was not considered during the prosecution process. Note, however, if the prior art is very similar to the prior art considered by the examiner during prosecution, it is unlikely that the threshold for a substantial new question of patentability will be met.

Within three months of establishing the re-examination board, a preliminary decision will be issued on whether or not a substantial new question of patentability is raised and the reasons for the same. If no substantial new question of patentability is raised, then the requested will be notified. However, if a substantial new question of patentability is raised, the patentee will be notified and the request will proceed to the second stage.

Second stage

The substantial new question of patentability is dealt with at the second stage.

Upon notification from the re-examination board, the patentee may choose to address the question(s) of patentability by submitting amendments to the claims. Amendments may include amendments to the description, drawings and/or claims. Note, that no proposed amendment may broaden the scope of protection.

The second stage must be completed within twelve months. At the completion of the second stage, the patentee will receive a certificate of re-examination, which may either cancel any claim determined to be unpatentable, confirm any claim determined to be patentable, or incorporate in the patent any proposed amendment determined to be patentable.

A patentee may appeal the decision of the re-examination board to the Federal Court within three months from the mailing date of the certificate of re-examination.

Impeachment proceedings

An action for the impeachment of patents can be brought in the Federal Court, by the Attorney General of Canada, or any interested person. An interested person has been broadly defined by the courts to include a competitor of the patentee who has received a cease and desist letter or accused of being infringing. Impeachment proceedings are typically brought by a defendant to an infringement action. The party choosing to invalidate a patent has the onus to prove that the patent is invalid on a balance of probabilities. The outcomes of an impeachment proceeding may be either a declaration by the Federal Court that the patent as a whole or a subset of the claims of the patent is void or, the patent as a whole is valid. Where a subset of the claims is declared void, the remaining claims may still be valid. Decisions of the Federal Court may be appealed to the Federal Court of Appeal.

The interested person challenging the validity of a patent has the burden of proof to show that the patent as whole or a subset of the claims is invalid. Interested persons may allege invalidity for several substantive reasons, including a lack of novelty, obviousness, inutility, non-eligible subject matter, overbroad claims (i.e., claims broader than the invention made or disclosed) and double patenting (i.e., the principle that there cannot be more than one patent granted for a single invention). For more information on subject matter that is patentable and patentability requirements, please visit our page on Patent FAQs -What is patentable? and Can I Patent My Idea? The Basics of Patentability in Canada respectively. For more information on double patenting, please consult our resource on Double Patenting in Canada.

Procedural reasons for invalidation may also be raised and include incorrect information in the statement of inventors or a petition. Note, however, that procedural reasons alone are unlikely to result in the successful impeachment of a patent.

An impeachment proceeding gives an interested person the right to appeal a Federal Court decision should the outcome of the invalidity action be unfavourable. In contrast, only patentees may appeal decisions rendered by the re-examination board.

Invalidating patents in the US

Inter partes review

One way to invalidate patents in the US is through inter partes review. An inter partes review involves the Board reviewing the patentability of one or more claims in a patent based on either anticipation under 35 USC 102 or obviousness 35 USC 103. The review would be based on prior art submitted by the requesting party. The prior art may consist of patents or printed publications.

Persons eligible to file an inter partes review include a person who is not the patent owner and has not previously filed a civil action relating to a challenge of the validity of claim or claims of the patent. A petition for inter partes review may only be filed after the later of: (i) 9 months after the grant of the patent or (ii) the date of termination of any post-grant review of the patent.

Initiating an inter partes review

For an inter partes review to be valid, the requesting party (i.e., petitioner) must complete the following:

  • identify all real parties in interest;
  • explain the grounds for unpatentability;
  • identify all claims to be challenged and the grounds on which the challenge to each claim is based including a claim construction for each challenged claim;
  • provide and explain evidence to be relied upon;
  • identify the grounds for standing; and
  • pay the requisite fee.

The requisite fee will depend on the number of claims of the patent to be subject to inter partes review. For requisite fee is $9,000 USD plus $200 USD for each additional claim over 20.

Inter partes review proceeding

Upon notification of a petition for inter partes review, a patent owner may choose to provide reasons against the commencement of an inter partes review by filing a preliminary response.

After receiving the petition, the Patent Trial and Appeal Board will decide whether or not to institute an inter partes review. The determination to institute an inter partes review will depend upon whether the petitioner has demonstrated a reasonable likelihood that he or she or it would prevail on at least one of the claims identified. Reasonable likelihood may be affected by whether or not the petitioner’s arguments are the same or substantially the same as those presented during the patent prosecution.

Once an inter partes review is instituted, the Board is statutorily required to complete the review within one year from the date of institution but the period may be extended up to six months if the Board has good cause. At the conclusion of an inter partes review, the Board will issue a final written decision on the patentability of the challenged patent claims and any new claims added by way of amendments.

Ex parte re-examination

Ex parte re-examination is another mechanism through which patents can be invalidated. Ex parte re-examination has a number of benefits. First, these proceedings tend to proceed more quickly and is less costly compared to validity litigation or inter partes review. Second, re-examination proceedings allow the use of the expertise of the Patent Office.

Any person may file a request for an ex parte re-examination at any time during the term of the patent. Once re-examination proceedings commence, only the patentee and the examiner are involved even if the request for ex parte re-examination was made by a third party (i.e., third party requester).

Once the Office receives the request for ex parte re-examination, they will determine, within three months, if a substantial new question of patentability has been raised. A substantial new question of patentability will be raised if a reasonable examiner considers the prior art raised to be important in deciding whether or not the challenged claims are patentable. If so, the re-examination proceeding will be ordered, and the patent in question will no longer be presumed to be valid under 35 USC 282.

Re-examination proceedings proceed in an ex parte manner. During re-examination, the Office will give claims the broadest reasonable interpretation. At the end of the re-examination proceeding, the Office will issue a re-examination certificate.

Compared to an inter partes review, ex parte re-examination is less costly. However, note that, for ex parte re-examinations, a third party requester cannot participate in the proceeding beyond filing a request for ex parte re-examination.


The validity of a patent may also be challenged through litigation. This is typically one of the responses of the defendant to a patent infringement action commenced in the Federal District Court. In order to succeed in invalidating a patent, the defendant (i.e., accused infringer) must show that each of the challenged claim is invalid. Consequently, it is possible that only a subset of claims are declared invalid by the court. The standard of proof for invalidating a patent is that of clear and convincing evidence, which means that the Court must find that it is highly probable that what the defendant seeks to prove (i.e., the claim or claims of a patent is invalid) is true.

Unlike ex parte re-examination proceedings, the court cannot amend patent claims during litigation. Note that an inter partes review cannot be initiated if an allegation of invalidity is raised in a patent infringement action.

There are several grounds for invalidation including the subject matter is not patent-eligible, the subject matter is not useful, the invention is not novel, the invention would have been obvious, there is a lack of enablement (i.e., the description is inadequate), the claims are indefinite and there is a double patenting at issue.

Generally, any person who invents or discovers any new and useful process, machine, manufacture, or composition of matter, or any new and useful improvement thereof, may obtain a patent. Process is defined as a process, act or method, which may include industrial and technical processes. Manufacture refers to articles made including manufactured articles. Composition of matter refers to chemical compositions or mixture of ingredients. Mere ideas or suggestions are not patentable subject matter.

For an invention to be useful, it must have a useful purpose and must be operative, that is, if an invention cannot perform its intended purpose, it would be inoperative.

For an invention to be novel, it must not have been described in a printed publication, or in public use, on sale, or otherwise available to the public before the effective filing date of the claimed invention and neither could it have been described in a patent issued or in an application for patent published or deemed published, in which the patent or application, as the case may be, names another inventor and was effectively filed before the effective filing date of the claimed invention. That said, however, there is a grace period of 1 year such that disclosure made 1 year or less before the effective filing date of the claimed invention falls within the exception.

Where the claimed invention is identical or nearly similar to the prior art, the claimed invention could be deemed obvious. The claimed invention must be sufficiently different from what has been used or described as set out in the prior such that a person having ordinary skill in the area of technology related to the invention may find the invention non-obvious.


If you would like assistance with invalidating patents, please feel free to contact us for a confidential and complimentary initial telephone appointment..