By Anthony L. Komaroff, M.D.

DEAR DOCTOR K:

My husband refuses to throw out pills that are past their expiration date. I think this is dangerous. I hope you'll convince him to clean out his medicine cabinet!

DEAR READER:

I understand your concern. But you may be able to cut your husband a little slack about his pills.

Believe it or not, there is relatively little scientific data about outdated medication. As pills get older, it's fair to ask two questions about them: Do they lose their strength, and do they become toxic or harmful?

There is little evidence that outdated medications are toxic or harmful. However, some drugs do lose their potency, or effectiveness, over time. The most notable is nitroglycerin, which should be replaced every six months. The epinephrine in EpiPens also loses its potency past its expiration date.

In addition, liquid drugs are less stable than tablets or powders. Liquid drugs include oral suspensions and solutions and injectable products.

Most drugs, however, retain their strength past their expiration dates. In one study, for example, researchers tested 96 different drugs stored in their original containers. They found that more than three-quarters of these drugs would remain stable for nearly five years beyond their expiration dates. And a study of two anti-influenza drugs found that these drugs remained fully active after 25 years of storage!

Drug companies generally give their products an expiration date two to three years from the date they're manufactured. Then, your pharmacist labels your bottle with an expiration date that's usually one year from the day your prescription is filled. So the expiration date you see on your pill bottle is usually sooner than the expiration date the drug company has assigned your pills.

Expiration dates shouldn't really matter with a medicine you get just once, treating a temporary problem -- like taking an antibiotic for strep throat, for example. You should swallow the last medicine long before its expiration date.

And they shouldn't matter for a medicine that you are supposed to take regularly for a chronic problem, such as to keep your blood pressure normal. Such medicine should never have an expiration date that already has passed. Unless, of course, you haven't been taking your medicine as prescribed. Then you do have a problem, but it's not with the expiration date.

Expiration dates should be an issue only when you have a medicine for a recurring, temporary problem. I'm thinking of a strong pain pill for back pain that flares up from time to time, for example, or an antibiotic for a recurrent urinary tract infection.

Remember that the favorable results I mentioned apply to medications that have been stored properly. Always keep your drugs in a cool, dry place in their original containers.

Never take a drug that looks, smells or tastes funny. And discard medications you no longer need. A tidy medicine chest will reduce the risk of errors.

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Dr. Komaroff is a physician and professor at Harvard Medical School. Go to his website to send questions and get additional information: www.AskDoctorK.com.

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