Stability testing

In brief

A stability study shows how the quality of an active substance or medicinal product changes over time under the influence of temperature, humidity and light. The results are used to derive the shelf life (for an active substance, the retest period) and the storage instructions that later appear on the pack. Because such a study runs for years and requires continuously monitored storage, many companies outsource it in full or in part to a contract laboratory.

A laboratory offering stability studies usually takes on three things: it stores the samples under defined conditions in qualified climatic chambers, it pulls them at the agreed time points and analyses them with methods that actually detect degradation, and it summarises the results so that they can be taken over into a marketing authorisation dossier or into the records of the ongoing stability programme.

When you need it

The most common reason is the marketing authorisation. A marketing authorisation application requires stability data on the active substance and the finished product, and because at least twelve months of long-term data are needed, these studies start long before submission. In clinical development, too, the shelf life of investigational medicinal products is demonstrated so that they may be used during the trial.

The obligation does not end with the authorisation. The manufacturer must continue to monitor the stability of its marketed product in an ongoing stability programme, and additional batches should be included after any significant change or deviation in the process or the packaging. Typical triggers are a different manufacturing site, new packaging material, a changed formulation or a change of active substance supplier. Anyone who wants to supply a product to countries with a hotter or more humid climate also needs data under the conditions of the climatic zone concerned.

A contract laboratory is especially worthwhile when your own chamber capacity is insufficient, when a company does not run its own GMP laboratory at all, or when studies are to be outsourced for a period in which your own laboratory is busy with other tasks.

Legal basis and rules

The relevant set of rules is the Q1 guideline series of the International Council for Harmonisation (ICH), which is adopted in the EU by the European Medicines Agency (EMA). In April 2025, ICH published a draft revision that combines the previous guidelines Q1A to Q1F and Q5C into one document. According to the ICH work plan from summer 2026, the final version is to be adopted at the end of 2026 at the earliest. Until it comes into force in the EU, the previous guidelines apply, and the following outline refers to them. For studies starting now, clarify with the laboratory how the transition will be taken into account.

Storage conditions and testing time points under ICH Q1A(R2)

The guideline distinguishes long-term storage, accelerated storage and, where necessary, an intermediate condition. For long-term storage in the general case, it provides for 25 °C at 60 % relative humidity or 30 °C at 65 % relative humidity, and for accelerated storage 40 °C at 75 % relative humidity. The intermediate condition of 30 °C at 65 % comes into play when the long-term study runs at 25 °C and a significant change occurs under accelerated storage. For products stored in a refrigerator or freezer and for products in semi-permeable containers, the guideline sets out separate conditions.

Under long-term storage, testing is usually carried out every three months in the first year, every six months in the second year and annually thereafter until the end of the proposed shelf life. Under accelerated storage, a six-month study requires at least three time points including the start and the end, for example 0, 3 and 6 months. For the marketing authorisation application, the guideline expects data from at least three primary batches that correspond to the later commercial product in process and packaging. For the finished product, at least two of these should be manufactured at pilot scale, and the third may be smaller if justified. At least twelve months of long-term data from these batches must be available at submission.

The long-term storage conditions depend on the climatic zone in which the product is to be marketed. For this purpose, the world is divided into zones I to IV, with the World Health Organization subdividing zone IV into IVa (hot and humid) and IVb (hot and very humid). ICH Q1A(R2) is tailored to zones I and II, which cover the EU, the USA and Japan. For supplies to tropical countries, the authorities there require data under stricter conditions.

Ongoing stability programme after authorisation

After authorisation, Chapter 6 of the EU GMP Guide requires an ongoing programme that shows the product in its marketed packaging remains within specification until the end of its shelf life. Unless otherwise justified, at least one batch per strength and per type of primary packaging is added each year, provided one was manufactured in that year. Out-of-specification results and atypical trends must be investigated. If a confirmed result affects batches already on the market, it must be reported to the competent authority. If the programme runs at a contract laboratory, a written agreement between the parties is required.

How the collaboration works

A stability study follows a fixed sequence that begins with the protocol and ends with the report. Because it can easily take several years, it is worth going through the steps with the laboratory beforehand.

What to look for when choosing a laboratory

Laboratories differ less in their basic equipment than in the range of storage conditions, the safeguards for the chambers and their experience with particular dosage forms. These questions help with the comparison:

Frequently asked questions

Sources

Every statement in this text was checked against these primary sources (as of 10.11.2026). Laws, guidelines and authority websites, no advertising.

1. ICH · ich-q1-draft-guideline-step-2-presentation-now-available-ic…
2. EMA · ich-q1-guideline-stability-testing-drug-substances-drug-pro…
3. ICH · ICH53_Q1_EWG_WorkPlan_2026_0818.pdf
4. ICH · Q1A(R2) Guideline.pdf
5. who.int · trs1010-annex10
6. ICH · quality-guidelines
7. EU-Kommission (EudraLex) · 2014-11_vol4_chapter_6_0.pdf
8. EU-Kommission (EudraLex) · eudralex-volume-4_en
9. EMA · ich-q2r2-validation-analytical-procedures-scientific-guidel…