Is it safe to take Flagyl pills a few years past the expiration date?

Hi Abe,
Thanks for your question.  Naturally, my professional answer would be NO.  One should never take expired medications.  In practice, however, if a medication had only just expired, it would generally be considered safe and probably still effective.  A drug's shelf life is determined by the time it takes for the active ingredient to degrade to 90% of its original content.  In other words, by the time the drug reaches its date of expiration, it should still have 90% of its active agent left.  Although the degradation by-products, themselves, are not usually harmful, the issue of whether the medication will still illicit that same response may be another matter.  But, generally speaking, at 90%, there still would be a good chance of the drug being efficacious.  However, taking a medication that has expired 'a few years ago' would not be prudent in my view.  The degradation process would have been uncertain during this time period, particularly if the drug had been exposed to fluctuating or extreme environmental conditions on storage.  

In addition, I am particularly reluctant to recommend the use of expired antibiotics.  Subtherapeutic levels of antibiotics encourage the growth of resistant bugs.  These so called 'resistant strains' develop a certain immunity to the antibiotic in question, and possibly to others similar to it.  This means that the infection becomes more difficult to treat and may become more widespread as a result.          

Abe, are you self-medicating, or have you self-diagnosed?  Oral antibiotics, such as metronidazole, should be prescribed by a doctor after he/she has thoroughly examined your condition.  This may have occurred a number of years ago when metronidazole was first prescribed for you, but it is worth having your condition reassessed by a physician so as to confirm a diagnosis, rule out any other underlying disorder, and of course, to determine whether metronidazole is indeed warranted.   Metronidazole has a relatively broad side effect profile, and so you wouldn't want to be taking it unless you really needed to.  If metronidazole in ultimately necessary, your physician will then be able to write up a fresh prescription for you.

I understand that it may seem wasteful to discard unused or expired drugs, particularly when medications can be so expensive these days.  But when it comes to antibiotics that have expired a few years ago, it would be the wisest and safest option.  I also appreciate that getting in to see a doctor can also be difficult and expensive, but this is also important.  Infections can lead to serious complications if left untreated.   

I wish you all the best, Abe.  


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Gisella Campanelli


I am able to answer questions relating to pharmaceuticals, therapeutic regimes and primary health care. This includes offering advice on drug indications, dosages, and disease state management. I can also identify side effects, drug interactions and contra-indications, and offer recommendations on ways to mitigate these. I can diagnose minor illnesses and suggest appropriate over-the-counter remedies and/or preventive healthcare tips. I can recognize cardinal symptoms which would otherwise require referral to a medical practitioner.


I am a registered pharmacist in Australia, and I have practiced in a hospital pharmacy for over thirteen years. My clinical specializations lie within the areas of psychiatry and general medicine (including gastroenterology, respiratory, endocrinology, neurology, infectious diseases, gerontology, dermatology). I self-managed the training program for pharmacy interns in preparation for their final registration exams, and I have worked for the Pharmacy Board of Australia as an examiner and exam writer.

I hold a Bachelor of Pharmacy from the Victorian College of Pharmacy, Monash University, and I am board-registered to practice within Australia. I also hold a Master's degree in an unrelated field (art conservation).

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