The ICH Q1A(R2) guideline on stability testing was last updated in 2003. That's twenty-three years ago. The iPhone didn't exist. Biologics were a niche. Gene therapies were academic papers, not approved products.
And yet, until April 2025, everyone in pharma was still referencing Q1A(R2) for long-term stability, Q1B for photostability, Q1C for new dosage forms, Q1D for bracketing and matrixing, Q1E for evaluation of data, Q1F for climatic zones (which was actually withdrawn in 2006 but people still cite it — I've seen this in two submissions this year). Plus Q5C for biologics, which lived in a completely separate document family.
Six documents. Some contradicting each other. One withdrawn. One that doesn't cover biologics at all. The system worked the way legacy systems always work: people who'd been doing this for fifteen years knew where to look, and everyone else was guessing.
ICH finally fixed it. Sort of.
What happened
In April 2025, ICH released a Step 2 draft of the new consolidated ICH Q1: Stability Testing of Drug Substances and Drug Products. One document replacing Q1A through Q1F and Q5C. Eighteen sections, three annexes, roughly five times the length of the original Q1A.
The comment period closed in August 2025. We're now waiting for Step 4 — the final version. Nobody I've talked to expects it before late 2026 at the earliest, but the draft is substantial enough that companies are already adjusting.
Here's what actually matters.
The big changes
Everything in one place
This sounds administrative. It isn't. When your stability protocol referenced Q1A for long-term conditions, Q1B for the photostability appendix, Q1D for your matrixing justification, and Q1E for the statistical approach — that was four documents. Four citation formats. Four sets of definitions that didn't always align.
Now it's one document with internal cross-references. The sections on drug substance stability and drug product stability in your CTD still point to the same data requirements, but the regulatory basis is now a single guideline.
Sounds small. Try maintaining SOPs that reference six separate documents and then tell me it's small.
Biologics are in
Q5C covered stability for biotechnological products. It was always the awkward cousin — written separately, structured differently, referenced reluctantly. The new Q1 pulls biologics into the main framework. Vaccines, gene therapies, cell therapies, advanced therapy medicinal products — all covered. Annex 3 is specifically for ATMPs.
If you're a biotech working on a biologic and your stability program was built on Q5C, you'll need to reconcile your protocols with the new structure. Not immediately. But before Step 4 hits.
Lifecycle stability management
This is the conceptual shift. Old Q1A was snapshot-oriented: you run your studies, you file your data, you set your shelf life. Done.
New Q1 treats stability as a lifecycle activity, aligned with ICH Q12. Your stability strategy evolves as your product matures. Development stability informs your registration program. Post-approval commitments feed back into your understanding of the product. On-going studies aren't just a regulatory checkbox — they're supposed to actually update your knowledge.
In practice, I think this means more justification for why you designed your stability program the way you did. Not just "we followed Q1A Table 1" but "here's the scientific rationale for our testing conditions, time points, and acceptance criteria." If you're already doing this, good. If your stability protocol is basically a template you copied from a previous submission with the product name swapped out — that's going to be harder to defend.
Risk-based study design
Bracketing and matrixing used to live in Q1D, a separate guideline that most people either loved or hadn't read. The new Q1 integrates these approaches directly and goes further — you can now formally justify reduced stability studies using risk-based design principles.
This is Quality by Design applied to stability. If you can demonstrate scientific understanding of your product's degradation pathways, you might not need to test every strength at every time point under every condition. ICH Q8, Q9, Q10, Q11, and Q14 are all referenced.
The catch: "risk-based" means you need to show your work. You can't just run fewer studies and call it risk-based. You need a documented risk assessment, and reviewers will read it.
New study categories
Old Q1A had long-term, accelerated, and intermediate. The new Q1 reorganizes this into formal and supportive:
Formal studies:
- Primary (your registration data)
- Commitment (post-approval, you promised FDA you'd run these)
- On-going (lifecycle monitoring)
- Product lifecycle (when you make changes)
Supportive studies:
- Photostability (formerly its own guideline, Q1B)
- In-use stability (new — what happens after the patient opens the bottle)
- Short-term / stress (excursions during shipping or temporary storage)
In-use stability is genuinely new territory. If your product is a multi-dose vial that sits in a clinic fridge for two weeks after first puncture, the new Q1 expects data to support that use period. This was always good practice. Now it's in the guideline.
Statistical modeling
Q1E covered statistical evaluation of stability data — shelf life estimation, poolability of batches, the regression analysis everyone runs but few people fully understand. The new Q1 updates the statistical approach and, based on the draft, attempts to be clearer about when you can pool data across batches and strengths and when you can't.
I say "attempts" because statistical sections in ICH guidelines are traditionally where clarity goes to die. But the new text is an improvement. The modeling guidance is more explicit about what methods are acceptable, which should reduce the back-and-forth with reviewers over whether your statistical approach was appropriate.
What this means for your CTD
Your Module 3 structure doesn't change. Section 3.2.S.7 still covers drug substance stability. Section 3.2.P.8 still covers drug product stability. Section 3.2.P.8.3 still holds your stability data.
What changes is the regulatory reference. Where your protocol currently says "conducted in accordance with ICH Q1A(R2)", it will eventually say "conducted in accordance with ICH Q1." Your SOPs need the same update. Your stability study reports need the same update.
More substantively: if your current stability program doesn't include in-use data, short-term excursion data, or a lifecycle management plan, you now have a gap that didn't exist under the old framework.
What to do now
The final guideline isn't out yet. But here's what I'd recommend based on what the draft says:
Now:
- Read the draft. It's 90+ pages but the first 30 cover the core changes. ICH Q1 Step 2 Draft (PDF)
- Inventory your current stability SOPs — which ones reference Q1A, Q1B, Q1D, Q1E, or Q5C
- Check whether you have in-use stability data for products that need it
- If you're filing an IND or NDA in 2026-2027, decide whether to reference the old guidelines or the new draft
When Step 4 drops:
- Update SOPs and protocol templates
- Retrain stability teams on the new framework
- Revise your stability sections in ongoing submissions
- Update your CTD cross-references
The uncomfortable question: If you're a small biotech and your entire stability program was built by copying a template from your last company, now is a good time to check whether that template actually covers what the new Q1 expects. Lifecycle management, risk-based justification, in-use stability — these aren't optional add-ons. They're the new baseline.
The Regfo angle
Our CTD Library currently maps requirements from ICH Q1A(R2) to Module 3 sections. When the final Q1 is published, we'll update every reference — the mapping stays, the guideline citations change. If you're using Regfo to check compliance, you'll see the updated requirements automatically.
The bigger value: the new Q1 creates exactly the kind of compliance gaps that are hard to catch manually. Your existing stability protocol was written to Q1A. The new Q1 expects things Q1A didn't. Which things? That depends on your product type, your dosage form, your target market. Cross-referencing a 90-page guideline against your specific situation is precisely what we built the compliance checker to do.
The ICH Q1 Step 2 draft is available at database.ich.org. Comment period closed August 2025. Step 4 (final) expected late 2026 or 2027.