ICH Q1 revision: for the first time since 1993, stability testing is about to really change. On 11 April 2025 ICH published the Step 2b draft of the new Q1 guideline "Stability Testing of Drug Substances and Drug Products", which consolidates the entire legacy Q1A-Q1F series and Q5C for biological products into a single document. The public consultation closed in summer 2025 and, according to the official Expert Working Group work plan, Step 4 adoption is expected in November 2026. For QA, QC and Regulatory, now is the right time to understand what changes and prepare the transition: in this article you will find the confirmed dates, the main changes and an operational checklist.
ICH Q1 revision: from eight documents to a single guideline
The ICH Q1 revision addresses a problem familiar to anyone who has ever set up a stability protocol: the requirements were fragmented across documents written in different eras. Q1A(R2) for formal studies, Q1B for photostability, Q1C for new dosage forms, Q1D for bracketing and matrixing, Q1E for the statistical evaluation of data, Q1F (later withdrawn) for climatic zones III and IV, plus Q5C for biotech products. The draft replaces them all with a single guideline organised into 18 sections and 3 annexes, designed to cover the entire product lifecycle.
The scope expands significantly: the new Q1 covers drug substances and drug products of both chemical and biological origin, including vaccines, advanced therapy medicinal products (ATMPs) and combination products, and incorporates guidance for all climatic zones to support global harmonisation. One single reference, where you previously had to navigate between guidelines, Q&As and regional practices.
The dates that matter: Step 2b, consultation and adoption
The official timeline can be reconstructed from ICH and regional authority documents:
- 11 April 2025: publication of the Step 2b draft and start of the public consultation across the ICH regions.
- Summer 2025: closure of the regional consultations (EMA collected comments until the end of July 2025; FDA closed its consultation on 25 August 2025).
- 2025-2026: the Expert Working Group works through the comments received, major ones first, then minor ones.
- November 2026: the target declared in the work plan for Step 3 sign-off and Step 4 adoption.
- June 2027: planned delivery of the official training materials and case studies.
Beware of a frequently misunderstood point: until Step 4 adoption and subsequent regional implementation (Step 5), the binding reference remains the current series. The draft should not be cited as a requirement in protocols, but it should be read now, because it already shapes long-term decisions: a stability study designed today will produce data that will be evaluated tomorrow, under the new guideline.
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What changes in stability testing
The classic framework - long term, intermediate and accelerated conditions, primary batches, commitment batches - is not overturned. What changes is the philosophy: from a set of prescriptive rules to a risk-based, lifecycle-oriented framework aligned with ICH Q12. The most relevant changes for those who design and evaluate studies:
| Area | Current series (Q1A-F / Q5C) | New ICH Q1 (draft) |
|---|---|---|
| Structure | 7 separate documents, written between 1993 and 2003 | Single guideline: 18 sections + 3 annexes |
| Scope | Small molecules (Q1A) and biotech (Q5C) treated separately | Chemical and biological products together, including vaccines, ATMPs and combination products |
| Reduced designs | Bracketing and matrixing in Q1D, applied cautiously | Lean, risk-based approaches formalised, with more room for justified reduced designs |
| Modelling | Statistical evaluation and extrapolation in Q1E | Enhanced stability modelling and clearer guidance on statistics and prediction |
| Lifecycle | Focus on initial registration | Lifecycle stability management integrated with ICH Q12, from primary batches to post-approval changes |
| Supportive studies | Photostability (Q1B); in-use and short-term barely covered | Photostability, in-use stability and short-term storage brought together in the same guideline |
In the public consultations, several stakeholders asked for more detail precisely on in-use studies, hold times and ATMP specifics: these are the areas to monitor in the final text, because they may be revised compared with the draft.
Transition checklist for QA, QC and Regulatory
The transition does not call for panic, but it does call for a plan. These are the steps we recommend starting now:
- Documentation gap assessment: compare SOPs, master protocols and stability policies against the Step 2b draft, flagging every point where you cite Q1A-Q1F or Q5C: they will need updating to the new references.
- Inventory of ongoing studies: classify active studies (registration, ongoing, follow-up) and assess which will reach completion under the new guideline.
- Assess the opportunities: enhanced bracketing, matrixing and modelling can reduce the analytical burden of your next protocols; build the risk rationale now.
- Align stability with ICH Q12: if you use established conditions and PACMPs, check how lifecycle stability management fits into your variations strategy.
- Train the team: plan QA, QC and RA training between adoption (expected in November 2026) and the arrival of the official ICH materials (2027), without waiting for the next inspection.
- Watch Step 4 and Step 5: assign one person to monitor adoption and EMA/FDA implementation, with a change control ready to open when the final text is published.
GuideGxP recommendation
Do not treat the ICH Q1 revision as a mere change of references in your documents. The value of the new guideline lies in the ability to defend leaner stability programmes in audits: those who reach adoption with a risk rationale already in place will genuinely reduce their testing burden, while those who simply update their SOPs will keep working as they did in 2003. Our operational advice: start the gap assessment by the end of the year, use the Step 2b draft as study material (not as a requirement) and focus on reduced designs and modelling, where the return on investment is highest.
For the full picture of the Q series - what is actually applicable today and how to prepare for the new Q1 - the GuideGxP guide Quality Guidelines ICH Q: what really applies, and readiness for the new Q1 includes a dedicated chapter on readiness for the new Q1, with ready-to-use Excel and Word toolkits.
