Taking expired aspirin is unlikely to harm you, but it probably won’t work as well as it should. Unlike some medications that become dangerous after expiration, aspirin’s main risk is reduced potency. The tablet gradually breaks down into weaker compounds over time, and that process accelerates depending on how you’ve stored it.
How Aspirin Breaks Down Over Time
Aspirin’s active ingredient, acetylsalicylic acid, is chemically unstable. It reacts with moisture in the air through a process called hydrolysis, splitting into two byproducts: salicylic acid and acetic acid. Salicylic acid is the compound aspirin was originally derived from. It still has some pain-relieving and anti-inflammatory properties, but it’s far harsher on your stomach. Acetic acid is essentially vinegar.
This breakdown happens slowly at room temperature but speeds up significantly with heat and humidity. Keeping aspirin in a bathroom medicine cabinet, where steam from showers creates a warm, humid environment, accelerates the process. A bottle stored in a cool, dry place will hold up longer than one exposed to those conditions.
How to Tell Your Aspirin Has Gone Bad
Aspirin gives you a clear sensory warning when it has degraded significantly. Open the bottle and smell it. If you detect a sharp vinegar odor, acetic acid has formed and the tablets have started to break down. The American Chemical Society notes this is one of the easiest ways to check whether old aspirin is still intact.
You can also look at the tablets themselves. Crumbling, powdering, or any change in color or texture are signs the chemical structure has shifted. If the tablets look and smell the same as when you bought them, degradation has likely been minimal, though not necessarily zero.
The Real Risk: Reduced Effectiveness
The primary concern with expired aspirin isn’t toxicity. It’s that you’re taking something that may not actually relieve your pain, reduce a fever, or deliver the anti-inflammatory effect you need. As the active ingredient converts to salicylic acid, each tablet contains less of the compound that makes aspirin work. You might take a full dose and get partial relief, or none at all.
This matters most in situations where aspirin’s effectiveness is critical. If you’re taking a daily low-dose aspirin for heart protection, a degraded tablet may not provide the blood-thinning benefit your doctor intended. If you’re reaching for aspirin during a suspected heart attack, you want a tablet that delivers its full dose immediately. In these scenarios, expired aspirin could give you false confidence that you’re protected when you’re not.
For a routine headache, taking a slightly less potent tablet is a minor inconvenience. For cardiovascular protection, it’s a real gap in care.
Stomach Irritation From Degraded Aspirin
Aspirin already carries a well-known risk of stomach irritation, and degradation makes this worse. Salicylic acid, the breakdown product, is more irritating to the stomach lining than aspirin itself. In fact, aspirin was originally invented in the late 1800s specifically to be a gentler alternative to salicylic acid. When your aspirin expires and reverts to that older compound, you lose that advantage.
If you’ve taken a single expired aspirin and feel fine, there’s no reason to worry. But regularly taking degraded tablets could increase your risk of stomach discomfort, nausea, or irritation compared to fresh aspirin.
What Experts Recommend
Harvard Health Publishing groups aspirin alongside liquid antibiotics, nitroglycerin, and insulin as medications that show signs of physical decay over time, recommending against using them past their expiration dates. MedlinePlus, the health information service of the National Institutes of Health, advises not taking expired medicines because they may not be as effective or their ingredients may have changed in ways that make them unsafe.
Many medications retain most of their potency well past their printed expiration dates. Aspirin is one of the exceptions. Its chemical instability makes it more prone to degradation than many other over-the-counter pills, which is why it gets singled out in guidance that otherwise takes a relaxed view of expiration dates.
How to Dispose of Old Aspirin
The FDA recommends using a drug take-back program as the best option for getting rid of expired medications. Many pharmacies and community organizations host collection events or maintain permanent drop-off bins. Some programs also offer prepaid mail-back envelopes.
If none of those options are available, you can dispose of aspirin in your household trash with a few precautions. Remove the tablets from the bottle, mix them with something unappealing like used coffee grounds, dirt, or cat litter, and seal the mixture in a resealable bag or container before throwing it away. This keeps the medication away from children, pets, and anyone who might go through the trash. Scratch any personal information off the original packaging before discarding it.