by Ernest Capraro

Created on: March 12, 2009

Before taking an expired pill, it is best to understand where those expiration dates come from.

Before any drug ever makes it to market, it goes through a lengthy review process involving a government agency. (In the U.S., that would be the FDA. Europe has it's own agency, as do Japan, Korea, and most any country you care to name.) The drug manufacturers (usually a pharmaceutical company such as Merck, Pfizer, or Eurand) are required to perform a variety of tests, all designed to present a safe drug product to the public. One small part of this testing is a stability study.

Stability testing allows the manufacturer to study how their pills (or syrups, or powders...) will stand the test of time. Batch of the pills are set aside in controlled, monitored environments. The selected environments will simulate storage conditions such as warehouses and supermarket shelves. They are monitored for temperature, humidity, and light exposure, as well as any other factors that may be considered significant to that drug. Stability studies will also be performed at elevated conditions, to see how the pill responds to less than optimal conditions and as way to predict in a short amount of time how the pill will perform in the long run. (A pill that remains unchanged under high temperature and humidity for a few months is likely to remain unchanged for years on a storeroom shelf.)

During stability testing, samples of the drug are regular taken and tested. Some tests deal with physical properties such as texture and taste, both of which can change with time. These affect how pleasant taking the drug is, but don't really affect its performance. More important are the tests for potency and impurities. Many drugs are unstable over lengthy periods of time, especially when heated, or exposed to light or moisture (humidity). In that case, the drug can break down, leaving less of the actual drug to perform its intended task. Worse is that sometimes the products of drug break-down (degradation) can be toxic. These materials are monitored by impurities testing. When they build up to an unsafe level in the pill, it would be poison for a person to consume it.

Expiration dates are set based on these three main factors.

1. When does the medicine begin to lose its appeal as a product?

2. When does the drug become too weak to function properly?

3. When does it become toxic?

Expiration dates are also set with a safety factor in mind. A pill isn't going to suddenly stop working on a set date. It's performance

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