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The SLEP Study Data

3 min read

The US military’s Shelf Life Extension Program (SLEP) tested stockpiled drug lots after their printed expiry dates, and the commonly quoted headline is that about 88% of the products examined kept their strength well beyond the label, by roughly 5.5 years on average. The result applies to sealed stock stored under controlled conditions and tested lot by lot, so it shows that expiry dates are cautious, not that any one salvaged bottle is still good.

Part of Shelf Life: Reality vs. Expiration Dates

The US military’s testing of stockpiled drugs past their dates is the best-known evidence that many medicines outlast their labels under good storage.

What The Program Did

SLEP is a US Department of Defense programme that holds very large stockpiles of medicines for military use. Instead of discarding stock at each printed expiry date, it tests samples of stored lots in a laboratory to see whether the product still meets its specifications, and extends the date where it does. More than 100 products have been examined this way.

The Headline Figures

  • About 88% of the products tested kept useful strength beyond the printed expiry.
  • About 5.5 years on average beyond the date.
  • Some products lasted well beyond the average.

These are the figures as they are commonly quoted. They have not been re-checked against the original reports for this article, and wording differs between summaries (some say the dates were extended rather than that full potency was retained), so use them as an approximate headline, not as a guarantee. They also leave the remainder of the products that did not qualify, which is a reminder that the result differs from drug to drug.

What The Data Do Not Show

Step 1: Note how the stock was kept. Stockpiles are stored under controlled conditions. A bottle left in a hot vehicle or a damp bathroom is not the same material, even if the printed date is identical.

Step 2: Note the unit of testing. Testing is by product and lot, with laboratory methods. Nobody can tell from a salvaged bottle which result applies to it.

Step 3: Note what is not being claimed. The programme does not show that every drug is stable. The exceptions in Medications That Genuinely Expire are real, and liquids, creams and suspensions are generally less stable than sealed solids.

Step 4: Use it as a reason to weigh, not to ignore, the date. The sound conclusion is “an expired date is not automatically a reason to discard a sealed solid tablet kept well”. It is not “dates do not matter”.

Common Mistakes

  • Quoting the percentage as a promise for any bottle. It describes a class of products tested under good storage.
  • Dropping the caveats about storage. The stock was well kept; yours may not have been.
  • Applying it to liquids and biologics. Those are the weaker cases.

Safety

Useful strength is not the same as full strength

Even where a drug stays within specification, its potency may be lower than a fresh product’s. For an antibiotic or an emergency drug, a weaker supply can fail without warning. The data say nothing about doses; use a reference for amounts, and do not assume that “still good” means “unchanged”.

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