Expired medication won't actually harm you or make you sick if you do take the expired medication.
However some medications begin to lose their potency and effectiveness after expiration date and the longer the medicine has been expired the less effective the medication becomes.
However some medications may still work just as good when expired so you don't have to throw out medication even when it's expired.
I've taken expired cold medicine and other expired medications before and they did me no harm.
My doctor said it was perfectly fine to take some expired medication and that it would not make me sick although it might not be as effective.