Every medicine has an expiry date printed somewhere on its packaging. Most people glance at it occasionally, perhaps while sorting through an old medicine cabinet. Few stop to think about how that date was determined. Yet behind every expiry date is a carefully designed program of scientific testing that helps ensure medicines remain safe and effective until the day they’re used.
Stability testing is a critical part of pharmaceutical development and manufacturing. It examines how medicines change over time under different environmental conditions, such as temperature, humidity and light. Internationally recognised guidelines, including those for ICH stability studies, help manufacturers generate reliable data to support expiry dates, storage instructions and regulatory approvals.
Why shelf life matters
Medicines are chemical and biological products, and they can change over time. Active ingredients may break down, lose potency or form impurities. The physical characteristics of a medicine, such as colour, texture or dissolution rate, may also change.
If a medicine degrades too much, it may become less effective or, in some cases, unsafe. Shelf life testing helps determine how long a medicine can be stored while still meeting quality standards. Accurate shelf life information protects patients, supports healthcare professionals and helps manufacturers maintain product quality.
What is stability testing?
Stability testing involves storing samples of a medicine under controlled conditions and testing them at regular intervals. The goal is to understand how the product changes over time and identify the conditions that best preserve quality.
Testing may evaluate factors such as the amount of active ingredient remaining, levels of impurities or degradation products, physical appearance, dissolution rate, moisture content, microbiological quality and packaging integrity. The data collected helps determine expiry dates and appropriate storage instructions.
The role of ICH guidelines
The International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use, commonly known as ICH, develops guidelines used by regulators and pharmaceutical companies around the world.
ICH stability guidelines provide a framework for designing stability studies, including storage conditions, testing intervals and data evaluation. Following these guidelines helps ensure that stability data is consistent, reliable and acceptable to regulatory agencies in different countries.
In Australia, the Therapeutic Goods Administration expects stability data to support the registration and quality of medicines.
Long-term and accelerated testing
Stability studies often include different types of testing conditions. Long-term stability testing stores samples under conditions that reflect the recommended storage environment. Samples are tested over months or years to observe how the medicine changes during its expected shelf life.
Accelerated stability testing exposes samples to higher temperatures and humidity than normal. These conditions speed up chemical reactions, helping scientists predict how the product may behave over a longer period. Intermediate conditions may also be used if significant changes occur during accelerated testing. Together, these studies provide a comprehensive picture of product stability.
Climate zones, packaging and product types
Medicines are distributed across the world, where climates vary widely. Temperature and humidity conditions in tropical regions can be very different from those in cooler climates. Stability testing takes these climate differences into account, helping manufacturers determine appropriate storage conditions and packaging for different markets.
Packaging plays a major role in protecting medicines from moisture, oxygen and light. Blister packs, bottles, desiccants and protective cartons are designed to help maintain product quality. Stability testing often evaluates the medicine in its final packaging to ensure the combination provides adequate protection throughout the shelf life.
Different types of products have different stability considerations. Tablets and capsules may be sensitive to moisture. Liquid medicines may be more prone to microbial growth or chemical degradation. Injectable medicines, vaccines and biological products may require strict temperature control, including refrigeration or freezing. Stability programs are tailored to the characteristics of each product.
Ongoing monitoring and what consumers can do
Stability testing doesn’t end once a medicine is approved. Manufacturers often continue monitoring commercial batches to confirm that products remain within specifications throughout their shelf life. Changes to manufacturing processes, formulations or packaging may also require additional stability studies.
Stability testing helps establish expiry dates, but proper storage is still important once medicines are in your home. Follow storage instructions on the label. Many medicines should be kept in a cool, dry place away from direct sunlight. Avoid storing medicines in bathrooms, where heat and humidity can affect quality, or in hot cars. Return expired or unwanted medicines to a pharmacy for safe disposal.
Every expiry date reflects careful scientific work designed to protect patient safety. Through stability testing and internationally recognised guidelines, pharmaceutical manufacturers can ensure medicines remain effective and safe throughout their intended shelf life. The next time you check an expiry date, you’ll know there’s a great deal of science behind that small printed label.