Category I, II, and III Regenerative Medicine Explained: How Japan Classifies Cell-Based Medicine

If you're researching regenerative medicine treatment in Japan, you may have come across terms like "Category I," "Category II," "Category III," or "MHLW-recognized." These aren't marketing labels — they refer to a specific legal classification system that Japan uses to regulate regenerative medicine before any patient is treated.

Japan created this framework because regenerative medicine — treatments that use a patient's own cells, donor cells, or cell-derived products — covers a very wide range of procedures with very different risk profiles. A treatment using minimally processed cells from a patient's own body raises different regulatory questions than one using pluripotent stem cells or gene-based technologies. Rather than regulate all of these the same way, Japan's Act on the Safety of Regenerative Medicine sorts them into three categories based on risk, and applies different levels of committee oversight to each.

Understanding this classification system doesn't tell you whether a specific treatment is right for you, and it doesn't substitute for a physician's individual assessment of your case. What it does is help you read regulatory information accurately — including understanding what a category assignment actually confirms, and, just as importantly, what it doesn't. In short: a category reflects the level of regulatory oversight a technology receives — not how well it works or whether it's the right choice for you personally. The sections below explain why.

What Is Japan's Act on the Safety of Regenerative Medicine?

Japan's Act on the Safety of Regenerative Medicine is the law that governs how regenerative medicine is provided in the country. The framework is designed to establish safety procedures and oversight requirements before a treatment can be offered to patients — it sets out how a treating medical institution must describe its intended treatment, screening process, and monitoring plan, and requires that description (called a "provision plan") to be reviewed by a certified committee before the treatment can be provided. Our guide to what a regulatory plan number actually certifies covers what happens once a plan is accepted.

The law separates two things that are easy to conflate: safety oversight and clinical implementation. Safety oversight is the review process itself — an institution submits its plan, a committee reviews it against the requirements that apply to that plan's risk category, and the institution may begin providing the treatment only once that review is complete. Clinical implementation is what happens afterward: the institution actually offering the treatment to individual patients, each of whom is separately assessed for eligibility by their own physician. A provision plan being reviewed and accepted is a precondition for offering a treatment — it is not the same event as a specific patient being treated, and it is not, by itself, a statement about how that treatment will perform for any individual patient. Our Safety & Regulation overview covers this framework in full.

Understanding Category I Regenerative Medicine

Category I is the classification the law reserves for regenerative medicine technologies it treats as carrying the greatest degree of uncertainty or potential risk. This generally includes technologies using pluripotent stem cells — such as induced pluripotent stem cells (iPS cells) or embryonic stem cells (ES cells) — as well as technologies using cells from another person (allogeneic cells) or from animals. Following a 2025 amendment to the law's subordinate regulations, Category I was also expanded to explicitly include in vivo gene therapy and related nucleic acid-based technologies.

Because of this classification, Category I provision plans must be reviewed by a "special certified committee" — a committee held to a more stringent set of composition and expertise requirements than the committee that reviews Category III plans. Category I is also the only category subject to a fixed waiting period: once a provision plan is submitted, the treating institution must wait 90 days from submission before the treatment can be offered, giving the review process time to run its course.

This reflects the law's risk-based oversight requirements, not a ranking of treatment quality — a point covered more fully in "Do Regulatory Categories Mean a Treatment Works?" below. It's also worth being direct about a related, separate point: a higher regulatory category does not mean a treatment is automatically more suitable for every patient. Suitability depends on an individual's own health history and goals, confirmed through physician review — not on which category a technology falls into.

Understanding Category II Regenerative Medicine

Category II covers regenerative medicine technologies the law treats as carrying a meaningful, but comparatively lower, degree of risk than Category I. Many cultured or expanded autologous cell therapies — where a patient's own cells are collected, cultured or expanded outside the body, and then reintroduced — fall into this category, though the specific classification depends on the details of the technology and process involved, not on the cell source alone.

Category II provision plans are reviewed by the same special certified committee tier that reviews Category I plans, though Category II is not subject to the fixed 90-day waiting period that applies specifically to Category I. For how this applies specifically to stem cell therapy, see our safety overview of stem cell therapy in Japan.

It's worth stating plainly here, since Category II is the tier many autologous cell therapies fall into: regulatory review evaluates compliance and safety considerations, not treatment effectiveness.

Understanding Category III Regenerative Medicine

Category III covers regenerative medicine technologies that don't meet the threshold for Category I or Category II — generally, minimally manipulated procedures using a patient's own cells. Category III provision plans are reviewed by a certified committee, a tier with less stringent personnel and structural requirements than the special certified committees that review Category I and II plans.

Category III still requires provision plan submission and committee review before treatment can be offered — it is a lower-oversight tier within a regulated system, not an unregulated one, and it should not be read as meaning a treatment in this category is unproven.

At a Glance: Comparing the Three Categories

This table summarizes oversight structure only. It doesn't rank the categories by outcome, and it isn't a substitute for reading the fuller explanation of what a category does and doesn't mean, below.

Do Regulatory Categories Mean a Treatment Works?

This is the question underneath most of what makes this classification system confusing, and it deserves a direct answer: no. A regulatory category — and committee acceptance of a provision plan — tells you that an institution's plan met the procedural requirements that apply to its risk tier. It does not tell you how well the underlying treatment works, or what evidence exists for a specific clinical outcome.

It helps to separate three different things that are easy to blur together:

• Regulatory oversight is a process check: does an institution's plan for screening, processing, and monitoring patients meet the law's requirements for its risk category?
• Scientific evidence is a separate question: what has research shown about a treatment's mechanism, safety profile, and outcomes, and how strong is that evidence?
• Clinical outcomes are what actually happens for an individual patient — which depends on that patient's own health status, the specific treatment, and factors no regulatory classification can predict in advance.

A treatment can have completed regulatory procedures while the underlying scientific evidence for how well it works continues to develop — these are not contradictory facts. Independent researchers reviewing Japan's committee-review system have also identified real limitations in how consistently that review is carried out: a 2023 peer-reviewed analysis found documentation gaps and potential conflicts of interest in a portion of the Category II plans it examined. This kind of finding doesn't mean the framework doesn't matter — it means that regulatory review, like any process carried out by people, has limits, and shouldn't be treated as a guarantee of outcome on its own.

How International Patients Should Interpret Regulatory Information

When you come across a regulatory category, a plan number, or the phrase "MHLW-recognized," it's reasonable to treat that as one piece of information among several — not as the whole picture. Alongside regulatory status, it's worth considering:

• What the treatment is actually intended to do. A specific claimed purpose is easier to evaluate than a general one.
• What evidence level supports it. Is there published research behind the specific approach being discussed, and what does that research actually show?
• What information the provider is willing to share. A specific category, a clear answer about provision-plan status, and a willingness to discuss both are reasonable things to expect from any institution.
• What a qualified physician says about your own case. Regulatory classification applies to a treatment technology in general; whether a treatment is appropriate for you specifically is a question only a licensed physician reviewing your history can answer.

This isn't a checklist for evaluating a specific institution's compliance — it's a starting point for the kinds of questions worth raising, and for reading regulatory claims accurately, whoever they come from.

How StemCellor Helps International Patients Understand the Process

StemCellor is a Japan-based medical coordination service for international patients. Where regulatory questions like these come up, StemCellor's role is to help organize the information, explain what a regulatory term generally means, and support communication between you and the licensed physicians or medical institutions who make the actual clinical and regulatory determinations for your case.

This coordination role has real boundaries. StemCellor does not itself hold or file a regenerative medicine provision plan, does not evaluate or rank other clinics' regulatory compliance, and does not make medical recommendations. A treatment's category, and whether it is appropriate for you individually, are confirmed by the receiving licensed physician or medical institution — not by StemCellor.

Frequently asked questions

What are Category I, II, and III regenerative medicine in Japan?

They are the three risk-based classifications Japan's Act on the Safety of Regenerative Medicine uses to sort regenerative medicine technologies, from Category I (the highest level of procedural oversight) to Category III (a lighter procedural tier). Each category determines which type of committee reviews a treatment's provision plan and what review requirements apply.

Does Category I mean a treatment is more effective?

No. The category system classifies the level of procedural oversight a technology's provision plan must go through — it does not rank treatments by how well they work. A Category I classification reflects a technology's assessed risk profile, not its clinical merit compared to Category II or III.

Does government regulation mean a treatment is proven?

No. Committee review under this framework evaluates whether an institution's provision plan meets applicable procedural and safety-process requirements. It is not a certification of clinical outcomes, and it does not replace independent scientific evidence about how a specific treatment performs.

What is the Act on the Safety of Regenerative Medicine?

It's the Japanese law that governs how regenerative medicine is provided, requiring treating institutions to submit a provision plan describing their screening, processing, and monitoring procedures for review by a certified committee before treatment can be offered.

Why do international patients need to understand these categories?

Because these terms appear often in materials about regenerative medicine in Japan, and they're frequently misread as claims about treatment quality. Understanding what a category actually confirms — and what it doesn't — helps you ask more accurate questions and read regulatory claims correctly, whoever they come from.

Who reviews a regenerative medicine provision plan?

Depending on the category, either a "special certified committee" (for Category I and II plans) or a "certified committee" (for Category III plans) reviews the plan. These committees are separate from StemCellor and from the treating institution's own management.

Does StemCellor decide which category a treatment falls under?

No. Category classification and provision-plan filing are the responsibility of the treating medical institution, confirmed through the committee review process described in this article — not something StemCellor determines or holds on any institution's behalf.

References

"Act on the Safety of Regenerative Medicine" (Act No. 85 of 2013, as amended), official English translation, Japanese Law Translation Database System, Ministry of Justice, Japan.

Tsunakuni I, Fujita M, Hatta T, Isobe T, Konomi K, Onishi T, Sanada S, Sato Y, Tashiro S, Tobita M. "Difficulties in ensuring review quality performed by committees under the Act on the Safety of Regenerative Medicine in Japan." Stem Cell Reports. 2023;18(3):613-617. DOI: 10.1016/j.stemcr.2023.01.013

Hosoya S, Ukon Y, Morita K, Minegishi E, Sugihara J, Hasegawa M. "Detailed revisions to the subordinate regulation following the amendment of the Act on the Safety of Regenerative Medicine in Japan." Regenerative Therapy. 2025;30:217-223. DOI: 10.1016/j.reth.2025.06.006