Basically a lot of chemical reactions go on in medication and the further past the expiration date the more the chemical make up could have altered. So simply put there is a possibility that its not the same anymore. Never take meds past the expiration date
Its hard to say for sure what the effects on the medication the expiry date has but i know with tylenol for example its not gonna be contaminated but it may not have the correct strength left in it... not saying if its expired you take more its jsut that it may not be as effective or it may be fine(you just dont know)... so i wouldnt reccomend it in any way as you may not get the correct dosing and as i dont know the exact effects the drug may have i wouldnt personally be the one to risk it and see what the effects might be... and to dispose of them its best to take them to the pharmacy for them to get rid of them properly... never throw them away or dump them down the drain...
You shouldn't use any medications that are expired.