When you have a splitting headache but realize the ibuprofen expired a year ago...
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You have a throbbing headache and open up the bathroom vanity to grab some acetaminophen or naproxen, only to realize those over-the-counter pain meds expired more than a year ago. Do you still take them? Run out to the store? Sit there and suffer? Consider this:

Is it safe to take expired medicine?

"As a general rule, there is no danger from taking a medication past its expiration date," says Robert Glatter, M.D., assistant professor of emergency medicine at Northwell Health and attending emergency physician at Lenox Hill Hospital. "The only conceivable risk is that the medication may not retain its original potency, but there is no danger related to toxicity of the medication itself or issues related to its breakdown or by-products." While different drugs will vary in expiration dates, the majority of OTC meds will expire within two to three years, he says. (What about expired protein powder? Learn about whether it's okay to use it or if you'll have to toss it.)

If you're curious about expired vitamins and supplements, here's a fun fact: Manufacturers of these products actually aren't required to put expiration dates on the labels, according to The New York Times. And that's, in part, because the FDA doesn't regulate vitamins and supplements. If manufacturers do decide to include a "best by" or "use by" date on a vitamin or supplement label, the rule is that they have to "honor those claims." Basically meaning, manufacturers are legally obligated "to have stability data demonstrating the product will still have 100 percent of its listed ingredients until that date," Tod Cooperman, president of ConsumerLab.com, told The New York Times. Translation: If you take a vitamin after it's "best by" or "use by" date, there's no guarantee it will hold it's original potency.

Why the need for expiration dates?

Expiration dates on drugs are required by the FDA, and they still serve a purpose. The goal is to let people know that medications not only are safe but also effective for patients, says Dr. Glatter. But many people just aren't sure about the safety associated with these dates, much less the efficacy. Plus, manufacturers aren't required to test a product's potency past its expiration date, so that's often an unknown variable. It's because of this gray area that most consumers tend to just discard pills that may otherwise be fine to take. And then they spend more money on new medicine.

Supplement companies aren't legally required to include expiration dates on their products' labels. Typically, the average shelf life for a bottle vitamins is around two years, but it can also depend on the type of vitamin, as well as where and how you store it. Don't get too hung up on this, though: Much like expired medicine, taking vitamins and supplements past their "best by" date won't cause any harm to your body; they just might be a little less potent. (Related: Are Personalized Vitamins Actually Worth It?)

There's one significant risk to consider, though.

While taking the expired medicine won't hurt you, the potency has likely diminished over time. Depending on the purpose of the medication, that can get risky.

"If you have strep throat, and are taking expired amoxicillin, the antibiotic will still work, but maybe at 80 to 90 percent of its original potency," which is sufficient to treat the infection, says Dr. Glatter. However, expired and weakened medications for serious health conditions or allergies can be a different story.

"EpiPens, for example, may be used past the expiration date up to a year, but the efficacy may be reduced by 30 to 50 percent in some cases," he says. "This could place some patients at risk who are suffering a severe allergic reaction or anaphylaxis," he says. (P.S. Is Expired Food Really Bad for You?)

And if you think you can just take double the dosage of expired OTC pain relievers to reach the effectiveness you're used to with less, just don't, says Dr. Glatter. "Never take any more than the recommended dose, as this could potentially lead to adverse effects on your kidneys or liver, depending on how the medication is metabolized or cleared from your body," he says. (Note that medications such as ibuprofen have warnings on the label regarding liver and kidney damage in relation to high dosages, so don't exceed the maximum daily allowance unless otherwise advised by a physician.)

The bottom line: Essentially all medications-vitamins and supplements included-may become slightly less potent as months or years pass, but that alone won't lead to any adverse side effects. "When a drug expires, the issue is that it may not produce the desired effect, whether it may relate to fever reduction, inhibiting the growth of bacteria or fungi, pain relief, or reducing blood pressure," says Dr. Glatter. "It's not that the expired drug itself is dangerous, or that there are toxic metabolites that could harm you." Consider the medication's purpose and what condition or symptoms it's treating, and discuss any potential dangers ahead of time with a physician. If a weakened drug could mean disaster for your health, head to the pharmacy or call your doctor immediately. Better yet, have a stash of important (and unexpired) meds at the ready for the next time a hangover (er, headache) hits.