Do medicines really expire? Can we use them after expiry date?

A controversial article titled “Truth about expiry date of medicine” is circulating on social media. It claims that drugs can be used safely after their expiry date. It begins with the statement, “Before 1979, medicines did not have expiry dates!” That claim is factually incorrect - any senior healthcare professional can confirm this. As a manufacturing pharmacist myself, I personally labelled medicines with expiry dates long before 1979.

The article argues that a study of large quantities of expired drugs found they retained 85–90 per cent potency, and therefore should not be discarded. Let us examine the truth behind this claim.

Why are expiry dates necessary?
Allopathic medicines are mixtures of chemicals. Even a single-ingredient medicine like paracetamol contains excipients to form tablets, injections, or syrups. These components can interact, especially if storage conditions are poor. Such interactions are slow and may only become visible after a long time.

Active ingredients degrade during storage, leading to loss of potency. Manufacturers acknowledge this on vitamin formulation labels with the note: “Appropriate overages are added to compensate for loss on storage.” Although not always stated, this applies to most formulations. Therefore, expiry dates are essential to ensure medicines remain safe and effective.

The above article claim that expiry dates exist only to make customers discard medicines and buy new ones, boosting sales. This is absurd. The expiry date is a double-edged sword. It not only inconveniences patients but also burdens manufacturers, who must accept unsold stock returned from retailers. For small and medium pharmaceutical companies whose products move slowly, this is a constant risk. Today, educated urban consumers often refuse medicines even two months before expiry and demand fresh stock. Manufacturers would prefer to avoid or extend shelf life if possible - but that is not scientifically feasible. Why?

How is the expiry date determined?
A manufacturer cannot fix an expiry date arbitrarily. It is set through scientific studies for each formulation, called ‘accelerated stability studies’. The medicine is stored under graded, adverse conditions - elevated temperature, humidity, and light - for 15, 30, 45, 60, and 90 days. Degradation is measured periodically through assays.

Quality assurance analysts study physical properties like colour, odour, taste, consistency or viscosity, along with chemical properties. Based on the rate of degradation, a probable expiry date is fixed. The Drug Standard Control Organization verifies and approves it. Note that only physical and chemical properties are tested, not therapeutic efficacy. Moreover, only the labelled active ingredients are estimated, not the degraded substances that may form under adverse conditions.

What factors affect medicine’s stability?
Three key factors influence a medicine’s stability:

Ingredients: Formulations are susceptible to environmental conditions, both external and internal. For example, many drugs oxidize when exposed to air, so antioxidants like BHA and BHT are added during manufacturing. However, not all manufacturers use them due to cost, relying instead on their process or assuming the ingredients are stable.

Method of manufacture: Good Manufacturing Practices (GMP) are critical. Hygienic or aseptic conditions, and inert atmospheres during filling, help ensure stability. Failure in these processes can lead to problems after the expiry date.

Storage conditions: Transport from manufacturer to retailer and subsequent storages are crucial. Some medicines require an unbroken cold chain. If that chain breaks, potency and safety cannot be guaranteed. Skilled pharmacists must handle medicines at every stage - from manufacture and analysis to storage and dispensing.

Why should expired drugs not be used?
Everyone involved - manufacturers, prescribers, traders, and dispensers – knows medicines degrade over time. The dangerous assumption is that degraded products are harmless. The article claims 85–90 per cent of the active ingredient remains after expiry. That may be true, but the critical question is: ‘What happened to the missing 10–15 per cent?’

As the law of conservation of mass states, matter is neither created nor destroyed. The lost active ingredient must have transformed into something else - possibly toxic chemicals. We cannot identify or estimate those unknown substances.

Pharmacopoeias and standard books like Merck’s Index list possible impurities for raw active pharmaceutical ingredients (APIs), but not for finished formulations, which are complex mixtures of active pharmaceutical ingredients and excipients. There are no tests for chemicals formed after expiry.

Moreover, formulations are trade secrets. Degradation products may differ even for the same drug made by different manufacturers. For example, different brands of paracetamol tablets may degrade differently. Analysing these degraded chemicals is extremely difficult, even today.

Why is analysis difficult?
Consider clinical blood drug concentration tests. Results are never 100 per cent accurate because the human body contains a “cocktail” of chemicals - excipients, enzymes, hormones, other drugs, and metabolites - all of which can interfere with analysis. It takes expertise, specialized methods, and reagents to eliminate these interferences. Not all laboratories can do it.

Hospital clinical pharmacists face these challenges when analysing body fluids, because human body is dynamic and blood composition changes every few minutes. That’s why the exact time of blood collection is recorded. Analysing expired medicines presents comparable complexity. So analytical reports on expired medicines cannot be taken at face value.

What should we do?
It is better to follow time-tested methods and practices rather than be swayed by pseudoscientific reports. Do not assume manufacturers set expiry dates merely to boost sales. Some pseudo-scientists plant such stories in journals, and a few years ago, editors of reputed European journals were prosecuted for publishing them.

Our own experience, observation, and analysis are the best guides, alongside established practices. As the great Tamil poet Thiruvalluvar said: “Epporul yaar yaar vaai ketpinum apporul maipporul kanpathu arivu”.

“Whatever you hear, from whomever you hear it, wisdom lies in discerning the truth of it.”