Why do medicines have expiry date?

Hey did you ever think about why do medicines have expiry date? We know that if it is any other product like food products, they get spoiled within some days and that is the reason for expiry date of the food, but what might be the reason behind expiry of medicines. Are you excited to know about it?  Then keep reading.

expiry date of medicines

Medicines are generally made up of variety of chemicals and that too in variety of ratios. Each medicine have its own chemical compositions. Now we know that chemicals have nothing like getting spoiled. There might be two reasons for the change of the behaviour of chemicals, they are

  1. The chemicals might react with themselves or might react with air.
  2. There is a special phenomenon in chemistry known as enantiomerism, this is the reason behind expiry of various types of medicines.

Not only these two reasons there might be other reasons also but these are important.

Now coming to the first reason, extreme care is taken while making medicines to prevent reaction of the chemicals with some other external substance, so that there is very less chance of chemical behaviour getting changed but still we cannot prevent reaction of some chemicals for long time so they can get spoiled.

Second reason is pretty interesting, enantiomerism is well known thing in organic chemistry. Many organic chemicals have different enantiomeric forms, simply they differ in their special arrangement and here among these two forms only one is biologically effective but not the other. Now some chemicals cannot be in the same enantiomeric form due to some electronic effects, they change into other form and establish an equilibrium where two forms exist in the same quantity.

When this happens the biologically effective form of the chemical decreases and thus medicine become ineffective or sometimes dangerous also, but generally we see that after changing its form also the medicine doesn’t become dangerous, it remains ineffective. The chemicals take time to change from one form to another and that time is put as the expiry date of the medicine.


For example brufen which is a well-known medicine for pain and fever have a chemical known as ibuprofen in it. The structure is shown below.


Now due to an electronic effect known as tautomerism near the acid group it changes to other form within sometime and thus this medicine gets some expiry date.

There might be some other reasons also but these two are basic ones.

So I hope that you got the answer to the question at least to some extent and I hope you like it.

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