Japan’s patent linkage system, which ties the regulatory approval of generic and biosimilar drugs to an evaluation of innovator patents, has come under renewed scrutiny amid legal challenges and growing calls for reform from domestic and international industry participants.
Japan’s patent linkage system, which ties the regulatory approval of generic and biosimilar drugs to an evaluation of innovator patents, has come under renewed scrutiny amid legal challenges and growing calls for reform from domestic and international industry participants.Earlier this month, the US-based Pharmaceutical Research and Manufacturers of America, or PhRMA, submitted a letter to Japan’s drug regulator, sharply criticizing the current framework. PhRMA argued that the system fails to provide timely notification to patent holders when follow-on product applications are submitted, raising concerns over market uncertainty and patent enforcement.
At the same time, Japanese regulators are engaged in policy reviews aimed at addressing operational inefficiencies and enhancing transparency within the system — signaling a pivotal moment for one of Japan’s complex pharmaceutical regulatory mechanisms.
— Patent linkage —
Patent linkage refers to a regulatory framework that connects drug approval processes with the status of existing patents. In Japan, when a generic or biosimilar manufacturer seeks marketing approval, the Ministry of Health, Labour and Welfare, or MHLW, assesses whether the proposed product could infringe patents held by the originator company.
This review is guided by MHLW-issued notifications, which aim to balance patent protection for innovators with the need to ensure a stable supply of affordable medicines. Under their guidance, Japan’s regulatory authorities will not approve a generic drug if the active ingredient is still under patent, but may grant approval for non-patented indications, provided the applicant excludes any patented uses and confirms this in advance.
Patent holders are encouraged to submit a drug patent information form to the country’s Pharmaceuticals and Medical Devices Agency, or PMDA, which along with the MHLW, reviews drug approval applications. Submission of this form is voluntary, and the information provided is not made publicly available.
While Japan’s system emphasizes an administrative review, other major jurisdictions rely more on judicial mechanisms to manage the intersection of patent rights and generic drug approvals.
In the US, the Hatch-Waxman framework requires generics to certify their position on listed patents, with disputes resolved through litigation. Europe limits regulatory involvement in patent issues, leaving enforcement to national courts.
Canada follows a similar linkage system to the US, combining patent certification with court-based resolution. In Australia and the UK, regulatory approval is separate from patent enforcement, which is handled entirely through the courts.
— Legal disputes over operational challenges —
Japan's heavy reliance on administrative judgment in resolving patent disputes and approving drugs has led to a series of prominent legal disputes that highlight the friction inherent in the current system.
In October 2024, the Tokyo District Court ruled on a challenge brought by Samsung Bioepis against Bayer Healthcare. In that dispute, Bayer had notified the MHLW and PMDA that the production and marketing of a biosimilar product could potentially infringe its patent — a product notably developed by an affiliate of Samsung Bioepis.
Samsung Bioepis argued that this notification harmed its business reputation and threatened supply stability. However, the court rejected the provisional injunction application, reasoning that patent infringement disputes under the patent linkage system are best resolved through administrative channels — with alternative remedies such as patent invalidation proceedings or administrative appeals available — rather than through immediate private litigation.
The Tokyo District Court’s ruling was in line with an earlier decision by the Intellectual Property High Court. In May 2023, the IP court ruled on a case in which Japanese healthcare company Nipro challenged the enforcement of patent rights by drugmaker Eisai and its subsidiary regarding a breast cancer drug containing eribulin mesylate.
Eisai had utilized the patent linkage system by integrating notification procedures that tied drug approval to the status of associated patents.
Nipro contended that these procedures created legal uncertainty by potentially delaying marketing approval of its generic drug and hindering its market entry. The court dismissed Nipro’s claims, effectively holding that even if an innovator’s patent might prevent a generic product’s approval, that risk is viewed as an administrative matter between the MHLW and the applicant — not a private dispute between competitors.
The IP court’s decision has been interpreted to suggest that generic manufacturers cannot seek pre-approval confirmation that their products do not infringe existing patents, which in turn prevents them from using the courts to resolve potential disputes in advance.
— Foreign pressure —
Critics of the Japanese system point out that the lack of publicly accessible patent information adds uncertainty for both originators and generic manufacturers.
In its submission to the US Trade Representative's Special 301 Report, the annual review of countries with inadequate IP policies, US lobby Biotechnology Innovation Organization in 2023 warned that Japan’s patent linkage mechanism allows generic drugs to be approved while patent disputes remain unresolved, undermining patent protections and innovation incentives.
More recently, the US Chamber of Commerce’s input for this year’s report (see here) included a recommendation to the Japanese government that legal disputes be handled by courts and that Japan adopt a more transparent linkage system with features like patent listing, disclosure, notification and a litigation-based stay period.
— Domestic concerns and policy initiatives —
While Japan’s patent linkage system was ultimately not included in the USTR’s IP review, its exclusion does not diminish the concerns raised by industry participants.
As legal battles and industry criticisms spotlight operational gaps in the system, policymakers are signaling a shift in approach. The MHLW has initiated a comprehensive review of the framework, exploring reforms aimed at enhancing transparency and reducing uncertainty.
One key recommendation calls for the establishment of an expert committee to examine and address issues in the current patent linkage system, including clarifying definitions and the scope of patents as they pertain to originator drugs.
It also recommended developing clear procedures and criteria for ascertaining patent infringement during the approval process for generic and biosimilar drugs, and to consider introducing a neutral expert consultation mechanism.
In response to these policy recommendations, PhRMA in its May 2 letter argued that the ministry is not “required or best-suited to determine whether a generic or biosimilar drug will infringe an innovator’s patents” and said that such decisions should be left to the courts.
A clearer division of responsibilities in Japan between the ministry’s administrative role and the court’s judicial determinations seems no closer.
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