Yurika Inoue
Mori Hamada & Matsumoto, Tokyo, Japan
yurika.inoue@morihamada.com

Yuta Kawasaki
Mori Hamada & Matsumoto, Tokyo, Japan
yuta.kawasaki@morihamada.com

Introduction

In Japan, two key regulatory frameworks protect the interests of brand-name drug companies: the re-examination system and the patent linkage system. The reexamination system restricts the entry of generic drugs for a certain period after the launch of the brand-name drug and, in practice, serves a function similar to data exclusivity, as generics cannot rely on or omit the submission of data originally filed for the relevant pharmaceutical, thereby precluding their market entry during that period. In addition, Japan operates a patent linkage system based on notifications issued by the Ministry of Health, Labour and Welfare (MHLW), rather than a formal statutory framework, under which the approval of generic drugs is coordinated with patents related to the brand-name drug.

This article provides an overview of the current reexamination system and patent linkage system, and examines recent revisions to the patent linkage system.

Overview of the reexamination system

In Japan, a reexamination system has been established for brand-name drugs with properties distinct from existing pharmaceuticals under the Article 14-4 of the Act on Securing Quality, Efficacy and Safety of Products Including Pharmaceuticals and Medical Devices (commonly known as the ‘Pharmaceuticals and Medical Devices Act’, or ‘PMD Act’). Under this system, for a specified period following marketing approval of brand-name drugs, the marketing authorisation holder must conduct investigations on the efficacy and safety (such as reports of adverse effect) of such drugs, and the Pharmaceuticals and Medical Devices Agency (PMDA) evaluates and reviews the results of such investigations to reexamine the efficacy and safety of the pharmaceuticals (Article 14-4 of the PMD Act).

The length of reexamination period for each brand-name drug is determined based on the notification by the MHLW, with guidelines established according to the type of pharmaceuticals, and may be extended for a period not exceeding 12 years from the date of marketing approval (Article 14-4(3) of the PMD Act) (Due to recent amendment to the PMD Act, the maximum period has been extended from 10 years to 12 years).

The Reexamination System as a De Facto Data Exclusivity Period

Under the Regulation for Enforcement of the PMD Act, applicants for marketing approval may omit certain data if the relevant matters are already well known in the medical and pharmaceutical fields. However, this exception does not apply where a product has the same active ingredients, dosage, administration, indications, and efficacy as a brand-name drug that is still within its reexamination period.

Therefore, during the reexamination period for a brand-name drug, generic drug companies would be required to submit data comparable to that of the brand-name drug, including clinical trial data. In practice, however, doing so is not economically viable, and generics do not pursue marketing approval during this reexamination period of brand-name drugs. As a result, this system effectively serves as a form of data exclusivity for brand-name drugs.

Patent linkage system in Japan

In Japan, a system – commonly referred to as the patent linkage system – operates to address potential conflicts with patents covering brand-name drugs during the review of generic drug marketing authorisation applications. The Japanese patent linkage system was introduced through an MHLW notification in 1994 and has been administered under a subsequent notification issued in 2009. It has no statutory basis and continues to operate on the basis of such notifications.

Under this system: (1) where a substance patent covering the active ingredient of a brand-name drug prevents the manufacture or marketing of a drug containing the active ingredient, generic drugs of such brand-name drug will not be approved; and (2) where a use patent covers only certain indications, effects, methods of use, or dosage of a brand-name drug, generic drugs may be approved if it is possible to manufacture or market a product for other indications or effects, provided that they do not seek approval for the patented indications or uses.

In practice, the Japanese system does not require comprehensive patent listing comparable to the United States Orange Book system. Rather, if a patent holder or the marketing authorisation holder of a brand-name drug wishes a substance patent or use patent to be taken into account during the approval review of generic drugs, a Pharmaceutical Patent Information Report Form must be submitted to the MHLW within the prescribed time period. Patents for which such form has not been submitted may, in principle, not be considered in the review process. This approach differs significantly from that in the US, where the patent linkage system is established under the Drug Price Competition and Patent Term Restoration Act of 1984 (the Hatch-Waxman Act) and is based on the mandatory submission and listing of patent information in the FDA’s ‘Approved Drug Products with Therapeutic Equivalence Evaluations’ (the Orange Book), a publicly available list of approved drugs and related patent information.

In addition, when generic drug companies seek to list products that may be subject to potential patent disputes on the reimbursement price list, they are required to coordinate in advance with patent holders or holders of marketing authorisation of the corresponding brand-name drugs and to proceed with the price listing process only where a stable supply can be ensured. However, in practice, even if such coordination fails, the generic drugs may still be listed upon application by the generic company.

Recent amendment regarding patent linkage system

At the end of 2025, significant revisions were made to the patent linkage system in Japan, as follows:

• First, follow-on biologics and biosimilars, which had not been explicitly covered previously but had effectively been treated as subject to the patent linkage system – have now been formally included within its scope.
• Second, while the system for submitting Pharmaceutical Patent Information Reports had already existed, the revisions introduced a clear submission deadline: such reports must be filed before the end of the reexamination period for the brand-name drug (or, if a relevant patent is granted thereafter, within 30 days from the publication of the patent gazette), and it is now explicitly stipulated that substance patents or use patents not reported in the form would, in principle, not be taken into consideration during the approval review of Generic Drugs for marketing authorisation.
• Third, the expert advisor system has been introduced. It has long been recognised that it is difficult for the MHLW to assess potential patent conflicts between brand-name drugs and generic drugs. In response, a pilot expert advisor system was implemented. Under this system, the MHLW shares relevant materials with a panel of expert advisors, comprising lawyers, patent attorneys and academics, and requests their independent assessment of the risk that a generic drug may infringe patents covering the corresponding brand-name drug. The expert advisors then provide a written opinion to the MHLW based on their assessment.

While the first two changes largely clarify existing practices, the third – the introduction of an expert advisor system – represents a more substantive development. When determining whether to approve generic drugs under the Japanese patent linkage system, the MHLW can now refer to expert opinions submitted by the expert advisors. The system is expected to be used primarily in cases where it is difficult for the MHLW to assess potential patent infringement, and such expert opinions are likely to influence approval decisions.

In this context, the procedures allow expert advisors to pose questions to the parties and request additional materials. The parties may respond and submit such materials within 30 business days, which may be a relatively short timeframe in practice. Accordingly, it is important for the parties to make full use of this opportunity to supplement their submissions.

Future outlook

Going forward, it will be important to closely monitor how these reforms are implemented in practice, such as the operation of the expert advisor system, as well as broader developments in the future direction of the patent linkage system in Japan, including potential legislation. While balancing the interests involved is not straightforward, continued consideration of appropriate approaches will be essential in light of their potential impact on the development of the life sciences sector.