By the PharmaTradz BD Team. Published October 2026.
The ICH stability guidelines are the internationally agreed rules for testing how the quality of a medicine changes over time under temperature, humidity and light, and for turning those results into a shelf life and storage instructions. The core document, ICH Q1A(R2), sets the standard test conditions: long-term storage at 25°C/60% RH or 30°C/65% RH, intermediate storage at 30°C/65% RH and accelerated storage at 40°C/75% RH. Companion guidelines cover light (Q1B), reduced study designs (Q1D) and data evaluation (Q1E), while WHO defines the climatic zones, including 30°C/75% RH for hot and very humid markets.
For a buyer, stability data answers one practical question: will this product still meet its specification on the last day of its shelf life, in your climate and in the pack you are buying?
The ICH Q1 family at a glance
ICH is the International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use, which writes guidelines that regulators then adopt. RH means relative humidity. Its stability guidance is split across several documents.
| Guideline | What it covers |
|---|---|
| Q1A(R2) | Stability testing of new drug substances and products: batches, storage conditions, test frequency and "significant change". Current version dated 6 February 2003. |
| Q1B | Photostability testing (1996) |
| Q1C | Stability testing for new dosage forms of an existing medicine |
| Q1D | Bracketing and matrixing designs that reduce the number of samples tested |
| Q1E | Evaluation of stability data, including how far a shelf life can be extrapolated (2003) |
| Q1F | Stability data for climatic zones III and IV; withdrawn in 2006 |
| Q5C | Stability testing of biotechnological and biological products |
Long-term, intermediate and accelerated conditions
Long-term (real-time) studies store the product under conditions that reflect its labelled storage and are the basis of the shelf life. Accelerated studies use heat and humidity to speed up chemical change, so problems show up within months. Intermediate studies, at 30°C/65% RH, are needed when long-term testing is at 25°C/60% RH and a "significant change" appears under accelerated conditions.
| Study (ICH Q1A(R2)) | Storage condition | Minimum data at submission |
|---|---|---|
| Long-term | 25°C ± 2°C/60% RH ± 5% RH, or 30°C ± 2°C/65% RH ± 5% RH | 12 months |
| Intermediate | 30°C ± 2°C/65% RH ± 5% RH | 6 months |
| Accelerated | 40°C ± 2°C/75% RH ± 5% RH | 6 months |
| Refrigerated: long-term | 5°C ± 3°C | 12 months |
| Refrigerated: accelerated | 25°C ± 2°C/60% RH ± 5% RH | 6 months |
| Frozen: long-term | −20°C ± 5°C | 12 months |
Q1A(R2) also asks for data on at least three primary batches, two of them at least pilot scale, tested in the container closure system proposed for marketing. Long-term samples are normally tested every 3 months in the first year, every 6 months in the second year and annually after that.
For a finished product, significant change means a 5% change in assay from the initial value, any degradation product exceeding its limit, failure of appearance or physical tests, failure of pH, or failure of dissolution for 12 dosage units. For generics containing well-known APIs, WHO's guideline accepts a lighter package: at least six months of long-term data on not less than two batches of at least pilot scale. National rules vary, so check yours.
Climatic zones I, II, III, IVa and IVb
Stability conditions depend on where a medicine will be sold. WHO divides the world into climatic zones by mean annual temperature and mean annual water vapour pressure, and gives each zone a long-term test condition.
| Zone | Climate | Long-term condition |
|---|---|---|
| I | Temperate | 21°C/45% RH |
| II | Subtropical and Mediterranean | 25°C/60% RH |
| III | Hot and dry | 30°C/35% RH |
| IVa | Hot and humid | 30°C/65% RH |
| IVb | Hot and very humid | 30°C/75% RH |
The history explains the split. ICH Q1F once set 30°C/65% RH for all of zones III and IV. Several countries in zone IV wanted a larger safety margin, Q1F was withdrawn, and WHO and regional groups defined conditions of up to 30°C/75% RH for hot and humid regions. WHO's current guideline, Stability testing of active pharmaceutical ingredients and finished pharmaceutical products (WHO Technical Report Series No. 1010, 2018, Annex 10), lists 25°C/60% RH, 30°C/65% RH and 30°C/75% RH as long-term options and says the choice depends on the climatic zone where the product will be marketed.
WHO also publishes a country-by-country list of required conditions. Its March 2021 update shows 30°C/75% RH for, among others, Brazil, Ghana, Indonesia, Malaysia, Nigeria, the Philippines, Singapore, Thailand and Viet Nam. WHO Prequalification expects shelf lives to rest on complete long-term data at 30°C/75% RH.
Photostability: ICH Q1B
Q1B checks whether light damages the product. The confirmatory test exposes samples to an overall illumination of not less than 1.2 million lux hours and near-ultraviolet energy of not less than 200 watt hours per square metre, alongside a dark control kept protected from light. Testing starts with the fully exposed product and moves to the product in its immediate pack, and then the marketing pack, only as needed. If the product is light-sensitive, the pack becomes part of the protection, and the label will usually tell users to protect it from light.
Setting the shelf life: ICH Q1E
Q1E explains how to turn stability results into a shelf life. Where results change over time, the shelf life is normally the earliest point at which the 95% confidence limit of the trend line meets the specification limit. It also limits extrapolation, which means claiming a shelf life longer than the real-time data actually covers.
Where long-term and accelerated data show little change and little variability, the shelf life can be up to twice the period covered by long-term data, but no more than 12 months beyond it. For refrigerated products the limit is one and a half times, and no more than 6 months beyond. Where significant change occurs at both accelerated and intermediate conditions, no extrapolation is allowed.
A worked example. A manufacturer has 18 months of long-term data at 30°C/75% RH on three batches of a tablet, plus 6 months at 40°C/75% RH, all showing little change. Twice 18 months is 36 months, but the 12-month cap allows only 18 + 12 = 30 months. So 30 months is the most it could propose. It must also commit to keep the studies running to confirm that shelf life. If the same tablet had failed at accelerated and at intermediate conditions, the shelf life could not go beyond the 18 months of real data.
Bracketing and matrixing: ICH Q1D
Bracketing tests only the extremes of a design factor, such as the highest and lowest strength or the largest and lowest fill volume, and assumes the levels in between are represented by those extremes. For example, 5 mg, 10 mg and 20 mg tablets made from the same blend in different weights could be covered by testing 5 mg and 20 mg. It is not appropriate when the strengths use different excipients, or when the chosen samples cannot be shown to be the true extremes.
Matrixing tests a selected subset of all the possible samples at each time point, so each batch is tested at some time points but not all. It should not be used when supporting data show large variability. Both designs are legitimate, but they need written justification in the dossier.
Ongoing stability after approval
Stability work does not stop at registration. Where the shelf life rests on extrapolated data, Q1A(R2) expects a commitment to continue the studies, and if production-scale data were not submitted, to place the first three production batches on long-term study.
Under EU GMP (EudraLex Volume 4, Chapter 6), every manufacturer runs an on-going stability programme to monitor the product over its shelf life. Unless justified otherwise, it includes at least one batch per year of every strength in every primary packaging type. Any confirmed out-of-specification result or significant negative trend affecting batches on the market must be reported to the competent authorities. Such results go through a formal OOS investigation. In the United States, 21 CFR 211.166 requires a written stability testing programme, including testing in the same container-closure system as the one in which the product is marketed.
The consolidated ICH Q1 revision
ICH is replacing the whole family with a single consolidated ICH Q1 guideline. The draft reached Step 2, the public consultation stage, on 11 April 2025, and the European consultation ran until 30 July 2025. It supersedes Q1A to Q1F and Q5C, extends the scope to vaccines and cell and gene therapies, and adds annexes on reduced designs and stability modelling, plus sections on short-term storage and in-use stability. It also sets out long-term conditions by climatic zone in one table, with 30°C/75% RH for zone IVb.
At the time of writing (October 2026), the draft has not reached Step 4, the final adoption stage. ICH's work plan targets Step 4 in November 2026. Until each regulator implements the final text, Q1A(R2), Q1B, Q1D and Q1E remain the guidelines in force.
Why hot, humid markets need zone IVb data in the registered pack
Air at 30°C and 75% RH carries roughly two-thirds more water vapour than air at 25°C and 60% RH. For a moisture-sensitive tablet, that difference can mean faster degradation, softening or slower dissolution. A product that passes comfortably at 25°C/60% RH may not last its full shelf life in a zone IVb warehouse or pharmacy.
The pack matters just as much. Stability data only applies to the container closure that was tested. A product registered in a high-barrier aluminium blister elsewhere cannot simply be shipped in a lower-barrier PVC blister, as our guide to blister packaging explains. Data at 30°C/75% RH in a different pack does not cover yours, and nor does data at 25°C/60% RH in the right pack. Good storage in transit, covered in our explainer on good distribution practice, protects the product but cannot make up for missing data.
What buyers should check
Which condition and zone? Ask for the stability summary, usually Module 3.2.P.8 of the dossier, and confirm the long-term condition matches your market. For a zone IVb country, that means 30°C/75% RH.
Which pack? Check that the data was generated in the exact primary pack you will buy and register: material, pack size and closure.
How much real data? Ask how many batches, at what scale and for how many months. Find out whether the shelf life rests on real-time data or on extrapolation, and whether the commitment studies are complete.
Light and reduced designs. Check the photostability result and any "protect from light" claim, and ask how any bracketing or matrixing was justified.
Ongoing results. Ask for recent on-going stability results, and whether any out-of-specification results or adverse trends have been found.
If your market uses the ASEAN format, see our comparison of CTD and ACTD for where stability data sits.
How PharmaTradz can help
Tell us your destination market and its climatic zone when you enquire, and we will ask manufacturers for stability data at that condition and in the pack you need. Our documentation and quality pack gathers stability summaries and other technical documents up front, or you can send us an RFQ directly. For other terms, see our pharma abbreviations A-Z.
Frequently Asked Questions(FAQs)
What are the ICH stability storage conditions?
Under ICH Q1A(R2), long-term studies run at 25°C/60% RH or 30°C/65% RH, intermediate studies at 30°C/65% RH and accelerated studies at 40°C/75% RH. Refrigerated products are stored long-term at 5°C ± 3°C, with accelerated testing at 25°C/60% RH.
What are the climatic zones for stability testing?
WHO defines five zones: I (temperate, 21°C/45% RH), II (subtropical and Mediterranean, 25°C/60% RH), III (hot and dry, 30°C/35% RH), IVa (hot and humid, 30°C/65% RH) and IVb (hot and very humid, 30°C/75% RH).
What is the stability condition for zone IVb?
The long-term condition for zone IVb is 30°C ± 2°C/75% RH ± 5% RH, and accelerated testing is at 40°C/75% RH. WHO Prequalification expects shelf lives to rest on complete long-term data at 30°C/75% RH.
How much can a shelf life be extrapolated under ICH Q1E?
Where long-term and accelerated data show little change, up to twice the period covered by long-term data, but no more than 12 months beyond it. Refrigerated products are limited to one and a half times and 6 months beyond, and no extrapolation is allowed if significant change occurs at both accelerated and intermediate conditions.
Has the new consolidated ICH Q1 guideline been adopted?
Not yet. The draft reached Step 2 for public consultation in April 2025, and as of October 2026 ICH's work plan targets final Step 4 adoption in November 2026. Until regulators implement it, Q1A(R2), Q1B, Q1D and Q1E remain in force.
