I took ibuprofen for a headache, but after taking it, I saw that the expiry date on the bottle was AUG-2015.

Well, taking the ibuprofen after its expiry date isn’t likely to harm you, but it may not be all that effective for your headache either. Drugs don’t “go bad” like bread or milk but that doesn’t mean it’s totally OK to use up your drugs after they’ve expired.

An expiry date is determined by the manufacturer and is meant to be the “use-by date.” This is the last day the manufacturer guarantees that the drug maintains its potency (effectiveness), purity, and physical characteristics. Drug manufacturers do a lot of testing to make sure their products are safe and effective, and this includes stability testing which determines expiry dates. The testing looks at whether the drug will still be potent within a specific timeframe not how long it takes for the drug to lose potency. The date is also based on the drug being stored under recommended conditions.

The expiry date shown on over-the-counter medications, like your ibuprofen, is often expressed as a month and a year – the drug is understood to be safe to use until the last day of that month, unless a specific day is shown. While prescription products don’t typically include expiry dates on the pharmacy labels, the products are assigned an expiry date by the manufacturer. It’s the pharmacist’s responsibility to calculate your prescription’s supply and ensure treatment will be completed before that date. If you want to know the expiry date of your prescription drug, you can ask for it.

Testing has been done on drugs past the expiry date – including some drugs that expired decades ago – to see whether they were still effective and safe. Interestingly the results found that the drugs still had a relatively high level of active ingredients; however, this varied depending on the type of drug, storage conditions, and type of packaging. While some drugs may retain potency far beyond the assigned expiry date, others will not.

So, if you’re considering taking a drug even though it’s past its expiry date, keep in mind that it might not be as effective. Consider why you’re taking it, for instance, if you’re treating a headache, it might not be such a big deal if the pain reliever isn’t as strong as it should be. But if you have an infection, it’s important that the antibiotic have the right potency. The bottom line is that if you inadvertently use a product after its expiry date, there’s not likely going to be a safety issue, but there’s no way of knowing whether or not it will be effective.

If you have expired drugs – prescription or over the counter – in your home, it’s a good idea to take them to a local pharmacy to be disposed of safely.