Hello and thanks for trusting me to help you and your pet today. I am a licensed veterinarian and would be happy to provide answers your questions.
I am not sure if you are referring to a tablet or a liquid formula, but it really doesn't matter. Shelf life or expiration dates are determined by the manufacturer and there is a huge range of variance. In general, tablet type forms would have a longer shelf life than most liquid forms, especially if compounded further into solution for flavoring for example. But, depending on how long it set on the shelf before you got it is a factor also. Without an expiration date listed on the bottle, there is no way to say how long the product would be expected to be effective.
That being said, most products do not "go bad". There may be exceptions with some liquid products, where there may be a concern for bacteria or rancidity. In most cases, if a tablet is beyond it's shelf life, it would not be any more harmful than the original product, but may be less effective than before it expired.
I hope this is helpful. If you would like any additional information or have additional questions please don't hesitate to ask!
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If they dispensed with a label, there should be an expiration date on it. Some clinics automatically list the expiration for one year from when it is dispensed, even if the stock bottle shows a longer date until it expires.
I personally have used products that are beyond the expiration date, in a pinch, so if an emergency occurred, using an expired product would not be a major problem until you could get your pet into see your vet, and as long as you were instructed how to use that particular product for that pet in the past.