Aspirin is acetylsalicylic acid. When it's exposed to water vapor, the acetyl group comes off and combines with water to make acetic acid, which is the acid in vinegar [1].

This happens pretty fast. An open bottle of uncoated aspirin tablets can start to smell of vinegar in a day or two, depending on the local relative humidity.

If you smell vinegar when you sniff your bottle of aspirin, toss the bottle. Why? Well, the other hydrolysis reaction product (salicylic acid) removes the outer layer of the skin and is used, for example, to remove warts [2]. Not something you want in your stomach.

[1] http://www.kii3.ntf.uni-lj.si/analchemvoc2/file.php/1/HTML/S...

[2] https://en.wikipedia.org/wiki/Salicylic_acid

I had always wondered why aspirin tended to smell like vinegar and rarely helped with headaches. It's quite satisfying to have an explanation for both.

In general, expired or unwanted medicine should be taken to a pharmacy or similar for proper disposal.

Isn't your stomach already extremely acidic...?

Not all acids are the same. What's at play isn't only the amount of free protons but also what else is disassociating. For instance, hydrofluoric acid is considered a weak acid but it can severely burn (pretty slowly but it will get you) or even kill you. The fluoride group will consume the calcium ions in your blood and possibly send you into cardiac arrest.

Any compound with a hydrogen ion that can dissociate in solution is technically called an acid, but that doesn't mean it's acidic properties are the most relevant.

Thanks, this is a great comment.

Sounds like a good argument for coating the pills.

This is a huge deal with drugs that can cost $10k per vial.

The manufacturers have no incentive to test for longer periods: it would just mean less revenue and more risk. And as I've mentioned before, physicians are very conservative and don't like stepping outside what other people do even if the basic research is there.

For example, the ability to pool leftover amounts of Yervoy (ipilimumab) among patients could save thousands of dollars each. The research so far shows that cancer drug Yervoy remains sterile, stable and effective for at least a month [1] but the manufacturer's guidelines say to use immediately after opening and throw away the rest. (Ironically the independent researchers couldn't afford to do a larger study because the vials were so expensive in the first place!)

It also limits how the drugs are delivered. For example, IL-2 (as a cancer immunotherapy) might be safer, more effective and more convenient as a single continuous infusion over a few weeks [2]. But the guidelines say to use immediately and throw away the excess.

It also limits research into what I think is the most promising near-term approach to cancer: intra-tumoral immunotherapy (with frequent low doses of e.g. ipi, nivo, IL-2 into lesions). Unfortunately this is way too expensive if you have to throw away 99% of a vial for each injection.

[1] https://www.ncbi.nlm.nih.gov/m/pubmed/26922168/

[2] https://www.ncbi.nlm.nih.gov/m/pubmed/10996039/

Bottled water has an expiration date.

280 million year old salt. Expires in 2019: http://imgur.com/a/Sug5c

It doesn't say it expires.

It says "mindestens haltbar bis", which is the German translation for "best before".

The manufacturer only guarantees the quality before that date. Afterwards, the anti-caking agent (Rieselhilfen) may not work so well, and the salt could be clumpy.

That's incredibly lucky, then. Imagine digging the salt out of the ground just before it expires, but still with enough time left to sell it.

I have read that water bottle contains expiry date, it is not for the water but to the plastic bottle which will start leaching chemicals after the expiry. I guess it is the same case here.

Even homeopathic medicine is required to have an expiration date, if only for legal compliance.

Homeopathic medicine should be required to actually have an effect, if only for legal compliance.

http://hpathy.com/ask-homeopathy-doctors/do-homeopathic-medi...

If you let the placebo effect count — and why wouldn't you? — it pretty surely will have some effect.

Even better, when combined with a consultation from a homoeopath, you're getting some informal counselling as well as a placebo. This is a pretty sweet combination, assuming you're not actually dying of something, and might keep you away from real pharmaceuticals with real side effects long enough to get better on your own.

(So my view is that homoeopathic remedies are very likely just sugar pills, but that it's far from clear we should be regulating them away on those grounds).

Haha. That is hilarious. 280 million years old, the preservative of preservatives. In many other countries (developing especially) they don't even pay attention to food expiration dates. We have eyes and a nose and they're really good at telling us when food shouldn't be eaten. I have a friend who is from Nigeria and was selling bags of rice at her shop. Food inspectors told her she had to throw the rice away because it had expired. She was devastated because she wasn't even used to thinking about rice expiring, especially not when it's just a few months old. Welcome to the West.

The "best before" time on the rice in my European cupboard is one year. It's still legal to sell it after that date [1]. The EU is considering[2] removing rice from the requirement to have a "best before" date at all, which is already the case for a few things[3], like salt and sugar.

[2] https://ec.europa.eu/food/safety/food_waste/eu_actions/date_...

[3] Annex X http://eur-lex.europa.eu/legal-content/en/ALL/?uri=CELEX:320...

[1] https://www.approvedfood.co.uk/ for example, you can search "rice".

Could also be related to the fact that they need to account for a massive range of storage conditions across all consumers. Some people live in climates where it hits 90-100+ degrees for many months of the year and may not have AC. Some people might keep their bottles on a counter that receives sunlight. And there are huge ranges in humidity. There's probably a big range in medicine lifespan between the best and worse cases there.

It's simply a guarantee of full potency of the drug. A while ago, a study (currently looking for it...) found ~90% of OTC drugs were perfectly fine 10+ years after the expiry date, IIRC. And most antibiotics should be just as stable as aspirin.

The US military operates the Federal Shelf Life Extension Program which, from what I understand, regularly tests federal stockpiles of medications to avoid waste.

http://www.astho.org/Programs/Preparedness/Public-Health-Eme...

Stability tests are actually pretty expensive, and you need to demonstrate that your shelf life is valid across the shelf life you request - so usually 2-3 years is about the max companies request, but it's good enough, and they need to ship their drugs out as fast as possible. Sometimes you see drug shelf life extensions post-release, but that's not always really worth the effort.

It is sort of a promise the drug will still work. Short expiries don't cost them sales and limit bad publicity and other hassles.

It shrinks the size of any recalls that may be required should something go wrong. (I don't know this for a fact, however.)