How old is too old for amoxicillin?

It depends. First of all, I would not take an antibiotic unless you know you actually have a bacterial infection. You could have a viral infection, or maybe not an infection at all. If you use the amoxicillin and you don't have a bacterial infection, you are likely increasing the chances that the amoxicillin will not work the next time you need it. This is because the bacteria that normally live in your body become resistant to drugs that they are exposed to over time. Then they are able to transfer this resistance to the bacteria that cause your infection, therefore preventing the antibiotic from clearing your infection. That said, if you do in fact know you have an infection that is bacterial and can be cleared by the amoxicillin, then how old is it exactly? The date on your prescription bottle is 1 year from the date it was filled. This date is assigned because the pills are being taken out of their original container. Some drugs may be good for a longer period of time if kept away from light and moisture. The expiration date assigned by the manufacturer (not the one on your pharmacy's label) is the date at which 90% of the active ingredient remains. So, worst case scenario, if you take an old drug, it may be much weaker than originally, and so it may not work. If the drugs looks different (as in changes in color or overall appearance) or smells funny or unusual, do not take it. Some drugs form harmful biproducts as they break down.