"Most of the time, 'sell by' dates are one of those things that look official, but you can probably ignore, like a child in a cop uniform," John Oliver said on Last Week Tonight earlier this year.

Apparently, it's largely the same with the expiration date on medication — you can probably ignore it.

Should you worry about expirations dates on medication?

The Food and Drug Administration (FDA) has since 1979 required that drug manufacturers place an expiration date on their medications. Seeing an expiration date would usually make someone think the product is useless after that date, but it turns out that's just the final date the manufacturer is willing to guarantee the product is still safe and reliable.

In fact, several incidents have shown medication can be effective for years after its expiration date.

Charles Williams / Flickr - flickr.com

The FDA initiated a study in 2006 that looked at the Department of Defense's drug inventory. Drugs obtained between 1986 and 2006 were analyzed, and the researchers found 88 percent of the drugs they looked at were still effective over five years after their expiration date.

Another study from 2012 looked at eight medications that had expired between 28 and 40 years prior and found almost all of them were still effective. The FDA lets drugs range between 90 and 110 percent of their advertised potency, and 86 percent of the drugs analyzed in the study had at least 90 percent remaining.

"Is the expiration date a marketing ploy by drug manufacturers, to keep you restocking your medicine cabinet and their pockets regularly? You can look at it that way," says a Harvard Medical School article from 2003. "Or you can also look at it this way: The expiration dates are very conservative to ensure you get everything you paid for."

Either way, they typically don't matter too much.

Certain medications like liquid antibiotics, insulin, and tetracycline do have more specific shelf lives, but most drugs do not. Many experts say that the main group of people who should care about expiration dates on drugs are people who regularly need drugs like insulin. If that Advil's been kicking around the house for a couple years, it probably still works.