EMA's New Active-Substance Guideline (In Force 1 Sept 2026): How to Justify Your Starting Materials Before the Deadline

Executive Summary

On 1 September 2026, the revised EMA Guideline on the chemistry of active substances (reference EMA/CHMP/QWP/49484/2026) comes into effect. It was adopted by the Committee for Medicinal Products for Human Use (CHMP) on 16 February 2026 and updates the first version published in 2016. The revision expands three areas that quality and regulatory teams cannot afford to treat as routine: the selection and justification of active-substance starting materials, the recovery and re-processing of materials and solvents, and the control of cohort-of-concern impurities, principally N-nitrosamines.

For active pharmaceutical ingredient (API) manufacturers and marketing authorization holders (MAHs) supplying the European Union, the practical message is direct. Every dossier that designates a starting material must carry a scientific justification that stands on its own, aligned with the principles in ICH Q11 and its Questions and Answers. Weak or generic starting-material rationales are one of the most common quality deficiencies EMA raises during assessment, and the revised guideline sharpens the expectation rather than relaxing it.

This is not only a European problem. Canadian API makers, contract manufacturers, and finished-product companies that export into EU supply chains, or that hold a Certificate of Suitability (CEP) or file an Active Substance Master File (ASMF), are pulled in through the same dossiers their EU customers submit and maintain. This guide explains what the guideline covers, what changed, how to build a defensible starting-material justification, and the steps to close the gap before 1 September 2026.

Introduction

Some regulatory changes rewrite the rules. This one raises the bar on evidence. The core concept of an active-substance starting material has not changed, but EMA now expects a clearer, better-argued, and better-documented case for the choices companies make at the very start of a synthesis.

The reason is history. Regulators learned the hard way that impurities can enter a drug substance far upstream of the final active pharmaceutical ingredient. The nitrosamine crisis that began with the sartan medicines showed that a control strategy is only as strong as its understanding of the full synthetic route, including the materials fed into it. Where a starting material is designated too late in the route, the steps that form and purge critical impurities sit outside the marketing authorization and outside routine good manufacturing practice (GMP) oversight. That is exactly the space where risk hides.

The revised Guideline on the chemistry of active substances responds to that lesson. It expands the sections on starting-material selection and justification, tightens the treatment of recovery and re-processing, and folds in current thinking on cohort-of-concern impurities. If your dossiers still lean on a short, template justification that a starting material is "commercially available" or "a significant structural fragment," this is the moment to strengthen the argument before an EMA assessor does it for you. For readers newer to the documentation itself, our primer on what a regulatory dossier is sets the context for where these justifications live.

What is the EMA Guideline on the Chemistry of Active Substances?

Direct answer: The Guideline on the chemistry of active substances (EMA/CHMP/QWP/49484/2026) is EMA’s scientific guideline setting out the chemistry, manufacturing, and controls (CMC) expectations for the active substance section of a marketing authorization application. It covers manufacture and process development, starting materials, characterisation, impurities, control strategy, specifications, analytical procedures, reference standards, container closure, and stability. It applies to the active substance information provided in module 3.2.S of the dossier, and to CEP applications and ASMFs. The revised version was adopted by CHMP on 16 February 2026 and comes into effect on 1 September 2026.

The guideline is the reference EMA assessors use when they review the quality data for a chemically synthesised or semi-synthetic active substance. It sits alongside the ICH quality guidelines, particularly ICH Q11 on the development and manufacture of drug substances, and applies whether the active substance details reach EMA through a full dossier, an ASMF, or a CEP granted by the European Directorate for the Quality of Medicines and HealthCare (EDQM).

What changed in the 2026 revision?

Direct answer: The 2026 revision keeps the familiar structure of the 2016 guideline but strengthens three areas. First, it expands the guidance on selecting and justifying active-substance starting materials, reinforcing the ICH Q11 principles. Second, it gives recovery and re-processing more detailed treatment, clarifying when reprocessing must be part of the described manufacturing process. Third, it adds recommendations on cohort-of-concern impurities, primarily N-nitrosamines, so the control strategy reflects current mutagenic-impurity thinking.

The revision does not throw out the previous framework. Companies that already maintain strong CMC documentation will recognise most of the content. What changed is emphasis and expectation. EMA has closed some of the interpretive gaps that let thin justifications through, and it has aligned the text with lessons from the nitrosamine experience and with ICH Q11.

Three practical shifts stand out for quality and regulatory teams:

• Starting-material justifications must be scientific, not administrative. Commercial availability alone was never sufficient under ICH Q11, and the revised guideline makes that expectation harder to sidestep.
• Recovery and re-processing need to be described and controlled. Where these operations touch quality, they belong in the dossier with proper justification, not in an undocumented shop-floor practice.
• Cohort-of-concern impurities are part of the starting-material conversation. Route knowledge, including the materials at the start of the route, feeds the nitrosamine risk assessment and the control strategy.

If your validation and qualification programme intersects with any of these changes, it is worth reading this alongside our analysis of the EU-GMP Annex 15 revision, because qualification evidence often supports the same control-strategy arguments assessors want to see.

Active-substance starting materials: how to justify your selection

Direct answer: To justify a designated starting material, apply the general principles in ICH Q11 and its Questions and Answers, and document the reasoning in your dossier. A defensible justification shows that enough of the synthetic route sits inside the described, GMP-controlled process to assure the quality and impurity profile of the final active substance. Commercial availability, cost, or supplier preference are not, on their own, acceptable reasons.

The starting material is the point at which GMP oversight and the marketing authorization begin. Designate it too late, and critical impurity-forming and impurity-purging steps fall outside regulatory control. That is why EMA assessors probe starting-material justifications so closely, and why a weak rationale so often triggers a major objection during assessment.

ICH Q11 sets out general principles that the revised EMA guideline reinforces. Use them as the backbone of your justification.

In practice, a strong justification package includes a clear synthetic route diagram from the starting material to the final active substance, the fate and purge of relevant impurities, the specifications and analytical procedures applied to the starting material, and a narrative that ties the choice back to each ICH Q11 principle. Where the active substance is semi-synthetic or derived from a biological or fermentation source, additional care is needed to define and control the source material.

MAHs relying on an ASMF or a CEP should not treat the starting-material justification as the supplier’s problem alone. The MAH remains accountable for the quality of the medicine, and an assessor’s objection to a starting-material rationale lands on the marketing authorization timeline. Coordinate early with your active substance manufacturer so the justification in the restricted part of the ASMF or in the CEP dossier holds up.

Recovery and re-processing under the revised guideline

Direct answer: The revised guideline gives recovery of materials and solvents, and re-processing, more detailed treatment. Reprocessing should comply with ICH Q7 or Part II of the EU GMP Guide. Where reprocessing is applied to most batches, it should be described as part of the standard manufacturing process. Occasional reprocessing should be clearly described in the dossier and justified with supporting data. Recovery operations that could affect quality must be controlled and documented.

Recovery and re-processing are areas where undocumented shop-floor practice quietly drifts away from the filed process. That gap is a classic inspection and assessment finding. If solvents are recovered and reused, or if batches are routinely reprocessed to meet specification, those operations affect the impurity profile and must be visible in the dossier and controlled under GMP.

The distinction the guideline draws is practical. A reprocessing step that happens for the majority of batches is really part of how the product is made, so it should be written into the described manufacturing process, not hidden as an exception. A genuinely occasional reprocessing event still needs to be described and justified, with data showing the reprocessed material meets the same quality standards. Recovered solvents and reagents need controls that ensure recovered material does not introduce impurities or carryover that the control strategy has not accounted for.

For quality teams, the CAPA lesson is familiar. When an investigation reveals that a recovery or reprocessing practice was never captured in the dossier or the batch records, the root cause is usually a documentation and change-control failure rather than a scientific one. Our guidance on why CAPA investigations keep failing applies directly: fix the system that let the undocumented practice persist, not just the single batch.

Cohort-of-concern impurities and N-nitrosamines

Direct answer: The revised guideline adds recommendations on cohort-of-concern impurities, principally N-nitrosamines, so that the active-substance control strategy reflects current mutagenic-impurity thinking under ICH M7. Applicants are expected to consider the maximum daily dose, route of administration, and treatment duration when building the control strategy, because these drive the acceptable intake limits for highly potent mutagenic impurities.

Cohort-of-concern impurities are a small group of highly potent mutagenic substances, including N-nitrosamines, for which the usual acceptable intake thresholds do not apply. The nitrosamine experience showed that these impurities can arise from the synthetic route, from recovered solvents, from certain reagents, and from starting materials, which is why the topic now sits inside a guideline about active-substance chemistry rather than only in standalone nitrosamine guidance.

The connection to starting materials is the point quality teams should internalise. A nitrosamine risk assessment depends on knowing the full route, including the materials at the start of it. If a starting material is designated late and the upstream chemistry is not described, the risk assessment is working with incomplete information. A well-justified starting material and a credible nitrosamine risk assessment support each other. For the Canadian and cross-border picture on limits and expectations, pair this section with our detailed article on nitrosamine impurities and Health Canada’s updated AI limits.

Who is affected, including Canadian exporters to the EU

Direct answer: The guideline affects anyone whose active-substance information reaches EMA: applicants and MAHs for human medicines in the EU, API manufacturers who supply them, and holders of CEPs and ASMFs. Canadian API makers, contract manufacturers, and finished-product companies exporting into EU supply chains are affected indirectly but materially, because their starting-material justifications appear in the dossiers, ASMFs, or CEPs their EU partners rely on.

For EU applicants and MAHs, the exposure is direct. From 1 September 2026, new applications and, where relevant, variations and dossier maintenance will be assessed against the revised expectations. A starting-material justification that would have passed under a lenient reading of the 2016 text may now attract a question.

For Canadian and other non-EU manufacturers, the exposure travels through the supply chain and the dossier. If you manufacture an active substance that is used in an EU-authorised medicine, your process description and starting-material justification are part of the regulatory record, whether through the restricted part of an ASMF, a CEP, or the applicant’s dossier. Expect EU customers to ask for stronger justifications, updated route information, and nitrosamine risk assessments that reference the materials at the start of the route.

The affected population, in short:

• EU applicants and MAHs for human medicinal products.
• API and intermediate manufacturers supplying EU-authorised products.
• CEP holders and ASMF holders.
• Non-EU manufacturers, including Canadian API makers and contract manufacturers, feeding EU dossiers.
• Regulatory affairs and CMC teams maintaining existing marketing authorizations.

Why weak starting-material justifications are a top deficiency driver

Direct answer: Starting-material justification is one of the most frequently raised quality deficiencies in EMA assessment because it sits at the boundary of GMP control and because a late designation can hide critical impurity chemistry. A weak justification delays approval, invites a major objection, and can force a company to redesign its described process late in the review, at significant cost.

In real assessments, the recurring objection is not that a company chose the wrong molecule as a starting material. It is that the justification does not demonstrate the choice against the ICH Q11 principles, or that critical impurity-forming steps sit upstream of the designated starting material with no described control. The consequence is a clock-stopping question that lands at the worst possible time in a submission.

From an experience standpoint, three patterns cause most of the pain. The first is the administrative justification, where commercial availability or a supplier relationship stands in for a scientific argument. The second is the short route, where a company designates a starting material only one or two steps from the final active substance to reduce the regulatory burden, leaving too little of the chemistry under GMP. The third is the disconnected nitrosamine assessment, where the risk assessment does not reference the upstream materials and therefore cannot credibly rule out a cohort-of-concern impurity.

The CAPA and remediation response is consistent. Reconstruct the full synthetic route, map impurity fate and purge across it, revisit the starting-material designation against every ICH Q11 principle, and rebuild the justification and the nitrosamine risk assessment as one connected package. Where a deficiency has already been raised, a structured, evidence-led response is far more persuasive than a defensive one. Our guide on responding to an FDA Form 483 or a Health Canada inspection observation sets out the same disciplined response approach that works for an EMA quality objection.

Starting-Material Justification Checklist

Use this checklist to test whether your dossiers are ready for the 1 September 2026 effective date. It doubles as a CMC gap-review tool.

• Confirm the revised guideline reference (EMA/CHMP/QWP/49484/2026) and the 1 September 2026 effective date are reflected in your regulatory intelligence log.
• Identify every EU dossier, ASMF, and CEP that designates one or more active-substance starting materials.
• For each starting material, confirm the justification addresses all ICH Q11 general principles, not just one.
• Verify that manufacturing steps affecting the impurity profile of the final active substance sit inside the described process.
• Check that each starting material has defined chemical properties, a specification, and appropriate analytical procedures.
• Confirm non-isolated intermediates are not being used as starting materials.
• Provide a complete synthetic route diagram showing the fate and purge of relevant impurities.
• For semi-synthetic or biologically derived actives, document the source and control of the source material, including any animal- or human-origin materials.
• Describe recovery of solvents and reagents, with controls that prevent uncontrolled carryover.
• Ensure reprocessing is described in the standard process where it applies to most batches, and justified where occasional.
• Confirm the nitrosamine risk assessment references the starting materials and upstream route, and reflects maximum daily dose, route of administration, and treatment duration.
• Align the starting-material justification and the nitrosamine risk assessment so they tell one consistent story.
• Coordinate with your API manufacturer or ASMF/CEP holder so the restricted-part content supports the justification.
• Log any changes through change control with impact assessment and approval.

Common Mistakes

Even mature CMC teams fall into predictable traps with starting-material justifications. These are the ones that most often trigger an EMA objection.

• Relying on commercial availability. Stating that a material is commercially available is not a justification under ICH Q11. Assessors want the scientific argument, not the purchasing rationale.
• Designating the starting material too late in the route. A short described process reduces the paperwork but pushes critical impurity chemistry outside GMP control and outside the marketing authorization. It is a false economy that assessors routinely challenge.
• Addressing only one ICH Q11 principle. Justifications that lean entirely on the significant-structural-fragment principle, while ignoring impurity control, isolation, and defined structure, are incomplete. The principles must be addressed together.
• Leaving recovery and reprocessing out of the dossier. Undocumented solvent recovery or routine reprocessing that never made it into the filed process is a common finding. If it affects quality, it belongs in the dossier.
• Treating the nitrosamine assessment as a separate silo. A risk assessment that ignores the starting materials and upstream route cannot credibly exclude a cohort-of-concern impurity. Connect the two.
• Assuming the ASMF or CEP holder owns the whole problem. The MAH remains accountable. A supplier’s weak justification becomes the MAH’s clock-stopping objection.
• Waiting until after 1 September 2026 to review. With the effective date fixed, a proactive gap review is far cheaper than a reactive response to a major objection during assessment.

Frequently Asked Questions

When does the revised EMA Guideline on the chemistry of active substances come into effect?

The revised guideline (EMA/CHMP/QWP/49484/2026) was adopted by CHMP on 16 February 2026 and comes into effect on 1 September 2026. From that date, it is the reference EMA assessors apply to the active-substance chemistry, manufacturing, and controls in a dossier.

What is an active-substance starting material?

An active-substance starting material is the point in a synthesis at which GMP oversight and the marketing authorization begin. Under ICH Q11, it should be a substance of defined chemical properties and structure that contributes a significant structural fragment to the active substance, with the impurity-relevant steps of the route described and controlled.

Why is starting-material justification such a common deficiency?

Because it marks the boundary of GMP control. If a company designates a starting material late in the route, critical impurity-forming and purging steps fall outside the described process. Assessors then raise a major objection, which can stop the review clock and force late redesign.

How do the ICH Q11 principles apply to my justification?

ICH Q11 provides the general principles for selecting a starting material. A defensible justification addresses them together: steps affecting impurities should be in the process, more of the route under GMP gives more assurance, the material is a significant structural fragment with defined structure, and non-isolated intermediates are not suitable.

How does the guideline connect to nitrosamines?

The revision adds recommendations on cohort-of-concern impurities, principally N-nitrosamines. Because these impurities can arise from starting materials, recovered solvents, and the upstream route, the starting-material justification and the nitrosamine risk assessment should be built as one connected argument, informed by maximum daily dose, route of administration, and treatment duration.

Does this affect Canadian companies that export to the EU?

Yes, indirectly but materially. If your active substance appears in an EU-authorised medicine through a dossier, ASMF, or CEP, your starting-material justification is part of the regulatory record. Expect EU partners to request stronger justifications and updated nitrosamine risk assessments ahead of the 1 September 2026 effective date.

How MFLRC Can Help

MF License & Regulatory Consultants helps API manufacturers, marketing authorization holders, and their CMC and regulatory-affairs teams turn the revised EMA guideline into a controlled, defensible set of dossiers rather than a scramble against the 1 September 2026 clock. Our senior consultants combine deep Health Canada and EU-GMP experience with hands-on CMC and quality expertise across pharmaceuticals, active substances, natural health products, cannabis, medical devices, and food.

For the EMA active-substance guideline specifically, we support:

• CMC and regulatory-affairs gap review against EMA/CHMP/QWP/49484/2026, testing each dossier, ASMF, and CEP for starting-material, recovery, reprocessing, and nitrosamine readiness.
• Starting-material justification memos that argue the designation against every ICH Q11 principle, with route diagrams and impurity fate-and-purge analysis, delivered through our regulatory affairs, licensing and import/export practice.
• Dossier remediation to strengthen module 3.2.S content, coordinate with ASMF and CEP holders, and respond to EMA quality objections with structured, evidence-led answers.
• Control-strategy and impurity support, including nitrosamine risk assessments connected to the starting-material argument, backed by our quality assurance and quality control services.
• EU-GMP readiness for the manufacturing and validation evidence that supports your control strategy, including the qualification themes we cover in our EU-GMP Annex 15 analysis.

With the EMA guideline in force on 1 September 2026, your starting-material justifications need to hold up now. Book a focused CMC gap review with MFLRC before the deadline.

Conclusion

The revised Guideline on the chemistry of active substances does not change what a starting material is. It changes how convincingly you have to justify the one you chose. From 1 September 2026, EMA assessors apply expanded expectations on starting-material selection, on recovery and re-processing, and on cohort-of-concern impurities, and they apply them to the dossiers, ASMFs, and CEPs that carry your active substance into the European market.

The companies that come through this smoothly will be the ones that treated the summer of 2026 as a window to review their justifications, reconstruct their routes, connect their nitrosamine assessments, and document their recovery and reprocessing practices before an assessor asked. The ones that struggle will be answering a clock-stopping objection in the middle of a submission. A focused gap review now is the difference between the two. Weak starting-material rationales are a known deficiency driver, and the deadline is fixed. The time to make your justifications defensible is before 1 September 2026, not after.

Sources and References

• European Medicines Agency: Chemistry of active substances, scientific guideline overview. ema.europa.eu
• European Medicines Agency: Guideline on the chemistry of active substances (EMA/CHMP/QWP/49484/2026). PDF
• ICH Q11: Development and Manufacture of Drug Substances. database.ich.org
• ICH Q11 Questions and Answers: Selection and Justification of Starting Materials. database.ich.org
• ICH M7: Assessment and Control of DNA Reactive (Mutagenic) Impurities. database.ich.org
• ICH Q7: Good Manufacturing Practice Guide for Active Pharmaceutical Ingredients. database.ich.org
• EDQM: Certification of suitability (CEP). edqm.eu