Medication expiration dates


Both OTC, prescription, and professional use vials. Why do they expire? What exactly causes them to be no good?

In: 1

Medications have chemicals in them. The chemicals have special shapes to them that makes them fit into specific places. The chemicals slotting into those places makes the thing we want the medication to do happen.

Over time, the shapes of chemicals change. We know after a certain amount of time a certain amount of the medication will have changed shape. The new shape doesn’t work the same way the old shape did – it probably won’t fit into the right slot, and it might go into a different slot and cause something bad to happen.

Expiration is when enough of a medication has changed shape that either wont have the right effect any more or will have a bad effect.

As for what causes it (less ELI5): heat and light both contribute to medications breaking down, because they’re both sources of energy. Energy can kick-start. chemical reactions that otherwise would not occur, even if overall the reaction is energetically favorable (“activation energy” is still needed for reactions that release more energy than they consume). Restricting the contact the chemicals have with air also helps, because some stuff in air can react with the molecules that are the active ingredient in medicine (water vapor, oxygen, etc).

Companies will do shelf life studies and accelerated shelf life studies to see how long a product will last.

They will literally sit some pills on a shelf at room temperature for a few years, test the chemical breakdown, and make sure the data is comparable to the original data.

They will also do an “accelerated” shelf life by sitting the pills at an elevated temperature (like 100 degree F), and test that after a few months. They will then do some kind of calculation (1 month at higher temperature equals 3 months at room temperature, for example.)

What the companies don’t do is test the pills to see when they expire; as long as the pills can last 2 years (or whatever their standard is), they are happy. So the pharma companies do not know if the pills can last 3, 5, or 10 years, and they don’t want to know. They want you to buy new pills, and a shorter expiration date covers their ass in case something unforeseen happens down the line.

I want to make it clear that none of the numbers I used should be taken as gospel. I made them all up just to explain the process.