Many Medicines Don’t Really Expire. So Why Do They Have Expiration Dates?

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When a piercing headache comes on, you reach for that ancient bottle of ibuprofen. But it expired, like, two years ago. Can you still take it? What's the worst that could happen? And why do over-the-counter medications -- or any meds -- expire in the first place?

What expiration dates mean (and what they DON’T mean)

Way back in 1979, the very same year McDonald's introduced the Happy Meal, the Food and Drug Administration put a rule on the books requiring drug manufacturers to stamp an expiration date on their prescription and over-the-counter products.

But the rule is tricky. Its meaning denotes that the manufacturer can guarantee the drug's safety and effectiveness up to the point of "expiration" -- but it doesn't indicate that the drug isn't safe or effective past the expiration date.

Confused? The expiration date tells you at what the point the manufacturer stops its testing of its product. If the aspirin in your medicine cabinet has an expiration date of two years post-manufacturing, it means that the company that made it only tested its lifespan over two years. After that, it's anyone's guess how it will perform.

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Is it safe to take expired drugs?

We tend to think of expired drugs the way we think of expired milk, "Will it make me sick if I put this in my body?" To an extent, that's fair -- if you notice a change in color, smell or texture, toss it, as those are good indications that something has gone off. The better way, however, to consider the safety of medication that's past its expiration date is to think about what will happen if the medication doesn't work.

To put it in more concrete terms, if you have a headache and you take a painkiller that has lost potency, you'll just be left with a headache. Though not ideal, that headache probably isn't going to be dangerous to you. On the other hand, if a condition requires you to take an anti-seizure medication, a drug that has lost potency could indeed be quite a danger to you.

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The exceptions to the rules

Given that, a good rule of thumb to follow is that the more crucial the medication is to your health and safety, the more diligent you'll want to be about checking and abiding by expiration dates. You'll also want to be more of a stickler when it comes to liquid medications, especially ones that list water as the first ingredient, as those will destabilize more quickly than their pill-form brethren.

There are also certain types of medications, like insulin and anticonvulsants, that shouldn't be used past the expiration date. Your doctor and/or pharmacist can assist you in learning which expiration dates should be more closely observed than others.

But, like, why is there an expiration date on my shampoo?

Cosmetic products like shampoo, acne treatments, sunscreen and even soap lose effectiveness over time due to exposure to heat and moisture. In the case of things like shampoo and soap, the result won't be much to worry about -- eh, so your hair doesn't get as clean as you might like, big deal. But if a product like sunscreen doesn't work, then you're in trouble in the form of a wicked sunburn.

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Jolie Kerr is a cleaning expert and diligent checker of expiration dates. Follow her @joliekerr.