SK Biopharmaceuticals Completes Japan Epilepsy Approval

SK Biopharmaceuticals has won Japanese marketing approval for cenobamate, its epilepsy drug, closing out a three-country regulatory sweep across Korea, China and Japan. The Ministry of Health, Labour and Welfare approved the drug, which will be marketed in Japan as Exkopri by partner Ono Pharmaceutical, on 16 September 2026 — three weeks after a Japanese regulatory council backed it for advancement.

Japan's epilepsy market in four numbers

~1Mpeople in Japan living with epilepsy, per trade-press framing of the approval

~30%of Japan's epilepsy patients not adequately controlled by existing anti-seizure medications

3Northeast Asian markets now covered — Korea, China and Japan

2019year the FDA first approved cenobamate in the U.S. as Xcopri

Figures from Korea Biomedical Review and Seoul Economic Daily's reporting of the 16 September 2026 announcement.

The last piece of a Northeast Asia puzzle

Japan is described repeatedly in Korean trade coverage as the world's second-largest single-country epilepsy market after the United States — a framing that comes from SK Biopharmaceuticals itself rather than an independently sourced market-research figure. Roughly 1 million people in Japan live with epilepsy, and about 30% of them do not achieve adequate seizure control on existing anti-seizure medications — the population cenobamate, as an add-on therapy, is aimed at. With Korea and China already secured, Japan was the market SK Biopharmaceuticals needed to complete its regional footprint before turning to actual sales.

How big Japan's epilepsy market gets by 2030

$598.9M → $883.7M

Japan epilepsy drugs market, 2024 actual to 2030 forecast, as estimated by Grand View Research.

2024$598.9M

2030$883.7M

Sources: Grand View Research, Japan Epilepsy Drugs Market Size & Outlook, 2025-2030

Regulatory News outlook

We'd expect cenobamate to take a modest but real slice of that growth — likely in the low tens of millions of dollars annually within a few years of launch — rather than displacing Japan's established second-generation anti-seizure drugs outright.

How we got here: Newer add-on anti-seizure drugs in Japan (brivaracetam, approved 2024) have typically taken single-digit percentage shares of the adjunctive-therapy segment within their first several years; applying that range to Grand View Research's $883.7 million 2030 Japan forecast implies an annual cenobamate opportunity in the tens of millions of dollars once launched.

A second regulatory step, three weeks later

Japan's drug approvals move in two steps, and cenobamate's followed the pattern. Japan's Pharmaceutical Affairs and Food Sanitation Council backed the drug for advancement on 26 August 2026; the MHLW's formal manufacturing and marketing approval followed on 16 September, three weeks later. Ono Pharmaceutical, which holds the Japan marketing rights, filed the underlying new drug application with Japan's PMDA on 30 September 2025 — meaning the full review, from filing to final approval, ran just under a year.

The approval rests on a genuinely regional trial, not a bridging study alone: YKP3089C035, a Phase 3 trial of cenobamate as adjunctive therapy, enrolled adults with partial-onset epilepsy uncontrolled on existing medication across Korea, China and Japan simultaneously, and met its primary efficacy endpoint — described in the sourcing available to Regulatory News only as a reduction in seizure frequency versus placebo, without a specific percentage disclosed for the Japan-inclusive population.

“Japan is a core market that must be secured for cenobamate's global growth, in terms of both treatment demand and market size. Now that the foundation for entering the major Northeast Asian markets linking Korea, China and Japan is complete, we will focus on producing commercial results that translate into actual prescriptions for patients in each market.” Lee Dong-hoon, President and CEO, SK Biopharmaceuticals — as reported by Korea Biomedical Review, 16 September 2026

One molecule, three brand names

Exkopri is not a new molecule reaching patients for the first time; it is a nearly decade-old drug reaching a new country. The FDA approved cenobamate in the United States in November 2019, where SK Life Science, SK Biopharmaceuticals' U.S. subsidiary, markets it as Xcopri. The European Commission approved it in March 2021 as Ontozry, marketed there by partner Angelini Pharma. By the time Japanese patients can access Exkopri, the drug will carry years of real-world prescribing experience in two other major markets behind it — a track record newer entrants in Japan's adjunctive-therapy category do not have.

What Exkopri brings to a crowded field

01

A trial built across three countries

YKP3089C035 enrolled Korean, Chinese and Japanese patients in the same Phase 3 program, giving Japan's regulators trial data from its own region rather than an extrapolation from a U.S.-only label.

02

Years of use elsewhere

Cenobamate has been marketed in the U.S. since 2019 and the EU/UK since 2021 under different brand names, giving Ono a real-world safety record to point to as it introduces Exkopri to Japanese prescribers.

03

A completed regional sweep

Japan's approval follows Korea and China within the same 10-month window, letting SK Biopharmaceuticals and Ono pursue a coordinated Northeast Asia launch rather than staggered, disconnected rollouts.

Exkopri against Japan's newer adjunctive therapies

Product	Marketer	Mechanism	Japan status
Exkopri (cenobamate)	Ono Pharmaceutical / SK Biopharmaceuticals	Sodium-channel and GABA-A activity	Approved 16 September 2026, adjunctive therapy
Fycompa (perampanel)	Eisai	AMPA-receptor antagonist	Approved for monotherapy and adjunctive use; long-established in Japan
Briviact (brivaracetam)	UCB	SV2A-binding	Approved June 2024, monotherapy and adjunctive

From company and regulator announcements; not a clinical comparison of efficacy.

Cenobamate's decade, one filing at a time

Cenobamate's road to Japan

1. 2011

   SK Biopharmaceuticals spun off

   Established as an independent company from SK Inc., then SK Holdings, to develop the group's central-nervous-system drug pipeline.

2. November 2019

   FDA approves cenobamate

   The U.S. approval launches the drug as Xcopri, marketed by SK Life Science.

3. March 2021

   EU/UK approval as Ontozry

   The European Commission approves cenobamate; Angelini Pharma markets it across Europe.

4. September 2025

   Ono files in Japan

   Ono Pharmaceutical submits the new drug application to Japan's PMDA on 30 September, under its 2020 licensing deal with SK Biopharmaceuticals.

5. November-December 2025

   Korea and China approvals

   Cenobamate is approved in South Korea in November and China in December, ahead of the Japan decision.

6. 16 September 2026

   MHLW approval

   Japan's Ministry of Health, Labour and Welfare grants formal manufacturing and marketing approval, completing the Korea-China-Japan sweep.

7. Ahead

   Japan commercial launch

   Ono Pharmaceutical has not published a specific Japan launch date.

What is not yet public: the specific milestone payment this approval triggers for SK Biopharmaceuticals, and Ono's launch timeline for Japan. Regulatory News will update this page if either is disclosed.

Frequently asked questions

What did Japan approve for SK Biopharmaceuticals?

Japan's Ministry of Health, Labour and Welfare approved cenobamate, marketed in Japan as Exkopri, as an adjunctive therapy for partial-onset (focal) seizures with or without secondary generalization in adults, announced 16 September 2026. Ono Pharmaceutical holds the Japan marketing rights under a 2020 licensing deal with SK Biopharmaceuticals.

Is this SK Biopharmaceuticals' first approval for cenobamate?

No. Cenobamate was first approved by the FDA in the United States in November 2019 (as Xcopri) and by the European Commission in March 2021 (as Ontozry, marketed by Angelini Pharma). Japan's approval follows South Korea (November 2025) and China (December 2025), completing SK Biopharmaceuticals' sweep of the three largest Northeast Asian markets.

How much is the Japan approval worth to SK Biopharmaceuticals?

The company has not disclosed the specific milestone payment tied to this approval, citing contractual terms. Its 2020 licensing agreement with Ono Pharmaceutical made SK Biopharmaceuticals eligible for up to JPY 48.1 billion in cumulative regulatory and commercial milestones plus royalties on Japan sales, a ceiling that is not the same figure as any single payment.

When will cenobamate launch in Japan?

No specific launch date was published alongside the approval announcement; Regulatory News did not find one in the sources reviewed.