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There are plenty of reasons to want a fully-stocked medicine cabinet — but it’s also possible to be too prepared. Like, while that huge bottle of aspirin you bought on sale ten years ago might have seemed like a great idea, it’s almost definitely expired by now.

Expired medicine might seem like a weird concept, because a lot of it doesn’t get moldy or slimy like old food. Some of it is just powder. But it can expire.

And when it does, it’s time to pitch it. Just like with packaged food, drug manufacturers in the U. S. are required to provide an expiration date for medications.

They’re estimated after seeing how samples of a drug degrade over short periods of time, or by accelerating the breakdown of the drug’s active ingredients. Like the dates on food, the dates on medicine aren’t an indicator of when the drug might hurt you. Instead, they’re a guarantee that it will work as intended, as long as it’s in the original, sealed packaging.

However, after that date, you can’t be totally confident that the medicine will work as well. And if you’ve already opened the bottle, the expiration date no longer applies, and all bets are off. Some of this is because outside factors can cause compounds in medicine to break down more quickly.

Heat, humidity, and sunlight are all big ones. And in some cases, those broken-down compounds can actually become unsafe. So if you’ve been keeping your aspirin in the bathroom cabinet all this time, your shower has probably done a number on it, even if everything looks normal.

For many medicines, there’s also the risk of bacterial growth, especially when it comes to liquid medicine. As soon as you open that container, the contents are no longer sterile, and quickly become susceptible to contamination from the environment. So if you take that past the expiration date, there’s a chance you’re drinking something pretty nasty.

Ultimately, taking expired medicine is like spinning a roulette wheel of potential dangers. In the best-case scenario, the drug just won’t work as well. And in the worst case, you’ll make yourself more sick.

And since it’s really difficult to figure out what all the risks are… it’s just not worth it. Also, this should go without saying, but this is especially true about drugs for serious or life-threatening medical conditions. Especially because some of those lose their effectiveness really quickly.

For example, the heart medicine nitroglycerine becomes unstable at high heat and is known to lose its potency fast. These drugs could also seriously hurt you. Some prescription drugs have a very narrow therapeutic window, meaning the exact dosage is really important.

Receiving too much or too little of an active ingredient could have significant adverse effects. So at the end of the day, it is much safer just to pitch things. If there aren’t any specific instructions on the package, the Food & Drug Administration website has recommendations for how to do that.

If you want to learn more, you can click the link in our description. Thanks for asking! And thanks to all of our patrons on Patreon for supporting this episode, and for asking such thoughtful questions.

If you want to help us keep making more episodes and support free science education online, you can go to patreon.com/scishow. {♪OUTRO♪}.